UNIVERSITY    OF    CALIFORNIA     PUBLICATIONS 

IN 

AGRICULTURAL    SCIENCES 

Vol.  I,  No.  12,  pp.  395-494,  plates  6-9  April  7,  1917 

CERTAIN  EFFECTS  UNDER  IRRIGATION  OF 
COPPER  COMPOUNDS  UPON  CROPS* 

l'.v   H,  11.  FORBES 


CONTENTS  page 

Part  I. — Experimental  Work 396 

Introduction   396 

Solid  wastes  397 

Soluble  copper  compounds 399 

Distribution  of  copper  compounds   throughout   the  Clifton-Morenci 

mining  and  Gila  River  irrigated  district    4iM 

Sources   of   copper 401 

Processes  by  which  copper  is  added  to  the  water  supply 402 

Table  of  solubilities  of  ''upper  compounds 403 

Copper  in  ores  and  tailings  from  Clifton-Morenci  district   405 

Dissolved  copper  in   river,  irrigating  and   ground   waters   below 

the    Clifton-Morenci    district 407 

Copper  in  soils  irrigated  with  tailings  waters 408 

Miscellaneous  soils  unaffected  by  mining  detritus 410 

Copper  in  vegetation  from  upper  Gila  farms 410 

Copper   in   vegetation    from   other  localities Ill 

Copper    in   flesh   and    bones   of   a    pig 4 1 2 

Distribution   of  copper   in    plants   with   root   systems  exposed    to   cop- 
per  compounds   4 13 

Corn  plants  grown  in  soils  containing  eopper 413 

Water    cultures    417 

Toxicity  of  copper  solutions  to  plant  roots  in   water  culture        419 

Stimulation    effects  in   water   cultures     422 

Effects  of  soil   upon  toxicity  of  copper  solutions 426 

Irrigation  experiments  428 

Cultural    experiments    432 

Pot  cultures  with  treated  soils 432 

Pot   cultures   with   field  soils 437 

Pot   and   plot   cultures 439 

Field  samples  of  soils  and  vegetation 440 

Use  of  copper  sulphate  to  kill  moss  in  irrigating  ditches II.'. 

Physiological  observations  on  toxic  effects  of  copper  salts 1  I  I 

Quantitative    work    I  I  I 

•  Paper  No.  31,  Citrus  Experiment  Station.  College  of  Agriculture.  Uni- 
versity of  California.  Riverside,  California. 


396      University  of  California  Publications  in  Agricultural  Sciences    [Vol.  1 

PAGE 

Reactions  of  copper  with  growing  points 450 

Varying  resistance  of  individual  cells  to  copper 454 

Diagnosis  of  copper  injury 454 

Part   II. — General    Discussion 458 

Preliminary  statement  $ 458 

Accumulations  of  copper 458 

Possible  effects  upon  health 460 

Amounts  and  significance  of  copper  in  aerial  vegetation 461 

Amounts  and  significance  of  copper  in  root  systems 463 

Relations   between  amounts   of   copper   in   root   systems  and   in- 
jury   to    plants 466 

Pathological    effects    467 

Soil  conditions  relating  to  toxic  effects  of  copper  upon  plants  ....  468 

Stimulation     470 

Field    observations    .: 472 

Effects  of  river  sediments 473 

Effect   of   cultivation   upon   alfalfa 474 

Summary  478 

Part    III. — Appendix 480 

Methods  of  analysis 480 

Reagents    and    apparatus 480 

Manipulation 480 

The  determination  of  copper  in  small  amounts  of  plant  ashes 483 

Bibliography    487 


Part  I.- EXPERIMENTAL  WORK 
INTRODUCTION 

The  region  to  which  the  studies  described  in  this  publication 
more  particularly  relate  lies  in  southeastern  Arizona  in  Greenlee 
and  Graham  counties  and  consists,  first,  of  the  Clifton-Morenci 
mining  district  and  second,  of  the  irrigated  lands  along  the  Gila 
River  from  twenty-five  to  sixty  miles  below.  The  Clifton-Morenci 
mining  district  is  drained  by  Chase  Creek  into  the  San  Francisco 
River,  which  in  turn  empties  into  the  Gila.  From  the  Gila,  be- 
ginning at  a  point  about  twenty-five  miles  by  channel  below 
Clifton,  irrigating  waters  are  withdrawn  for  the  use  of  the  rich 
lands  extending  somewhat  discontinuously  from  above  San  Jose 
to  Fort  Thomas,  a  distance  of  thirty  miles.  For  about  forty 
years,  this  up-stream  mining  district  and  the  irrigated  lands 
below  have  developed  together  from  small  beginnings  into  large 
industries. 

Beginning  with  the  initiation  of  smelting  operations  on  the 


L917]     Forbes:  Irrigation  Effects  of  Copper  Compounds  Upon  Crops      397 

San  Francisco  River  in  1882,  comparatively  small  amounts  of 
mining  detritus  musl  have  found  their  way  into  the  irrigating 
water-supply.  Following  the  discovery,  in  is!):},  of  immense 
deposits  of  Low-grade  sulphide  ores  in  the  district  and  the  erec 
t i'ui  of  concentrating  plants  to  handle  them,  rapidly  increasing 
quantities  of  fine  slimes  were  discharged  into  the  stream  How. 
becoming  noticeable  in  the  irrigating  waters  of  Graham  County 
about  the  year  1000.  Following  the  observation  of  their  pres- 
ence, various  crop  failures  were  attributed  from  time  to  time  to 
the  tailings,  resulting  finally  in  a  request  by  the  farmers  of  the 
district  to  the  writer,  for  an  examination  of  the  facts  relating 
to  damage  done  by  mining  detritus  to  their  irrigated  crops. 

Solid  W  \stes 
Following  this  request,  the  writer  began  a  study  of  the  prob- 
lem in  .May,  1904,  which  resulted  in  the  publication  of  Bulletin 

53  of  the  Arizona  Agricultural  Experiment  Station.  September 
20,  1906.  This  publication  established  the  fact  that  irrigating 
sediments,  in  general,  may  be  beneficial  or  harmful  according  to 
their  composition  and  physical  character  and  to  the  manner  of 
their  disposition  in  or  upon  the  soil.  If  allowed  to  accumulate 
upon  the  surface  of  the  soil  in  the  form  of  more  or  less  im- 
pervious silt-blankets,  their  influence,  by  limiting  the  supply  of 
water  and  air  to  the  soil,  is  notably  harmful.  Tn  the  ease  of 
the  mining  wastes  from  the  Clifton-Morenci  district,  which  are 
particularly  plastic  and  "tight"  in  character,  the  damage  done 
was  found  to  be  greater  than  that  resulting  from  sediments  aris 
ing  from  ordinary  erosion.  It  was  determined  that  the  damage 
from  these  wastes,  particularly  to  alfalfa  and  other  crops  which 
cannot  receive  constant  and  thorough  cultivation,  was  of  an  in- 
creasingly serious  character. 

The  farmers  of  Graham  County,  represented  by  one  of  their 
number,  finally  brought  suit  against  the  Arizona  Copper  Com- 
pany. Limited,  for  discharging  tailings  into  their  irrigating 
water-supply.  The  case  was  decided  in  the  District  Court  of 
Graham  County  in  favor  of  the  farmers,  and  an  order  was  issued 
in  November,  1907,  effective  May  1,  190S.  restraining  the  mining 
companies  from  discharging  "slimes,  slickens  or  tailings"  into 


398      University  of  California  Publications  in  Agricultural  Sciences    [Vol.  1 

Chase  Creek,  the  San  Francisco  River,  or  the  Gila  River.  The 
case  was  appealed  to  the  territorial  Supreme  Court  where,  how- 
ever, the  decision  was  confirmed  in  March,  1909.  The  case  was 
again  appealed  by  the  Arizona  Copper  Company  to  the  Supreme 


i  -     v .. "y7~, 


Fig.   1. — General  map  of  the  Clifton-Morenci   and  Gila   River  mining   and 
irrigation  district,  Arizona 


Court  of  the  United  States,  where  it  was  again  and  finally  de- 
cided in  favor  of  the  farmers  on  June  16,  1913. 

During  and  since  the  occurrences  above  mentioned,  large 
quantities  of  solid  wastes  have  been  impounded  by  the  copper 
companies  in  settling  basins  constructed  for  their  storage  in  the 


1!H7|     Forbes:  Irrigation  Effects  of  Copper  Compounds  Upon  Crops      399 

district.  Recent  investigations  by  the  companies  indicate  a  pos- 
sibility that  with  copper  at  15  '-nits  a  pound  these  stored  tailings, 
which  average  about  0.85  per  cent  copper,  may  be  profitably 
reworked. 

Tn  the  long  run.  therefore,  it  may  be  found  that  an  adjust- 
ment based  upon  a  complete  and  impartial  statement  of  facts 
relating  to  the  tailings  situation  is  beneficial  both  to  the  agri- 
cultural and  to  the  mining  interests  concerned. 

Soluble  Copper  Compoi  nds 

Following  the  disposition  of  mining  detritus,  there  remained 
the  problem  of  soluble  copper  compounds  which,  in  small  but 
continuously  appreciable  quantities,  find  their  way  with  waste 
waters  into  the  si  ream-How  of  the  region.  These  compounds 
originate  in  the  ores  of  the  district  and  are,  as  in  the  case  of  the 
carbonates,  directly  soluble  to  a  slight  extent  in  drainage  waters, 
especially  in  the  presence  of  carbon  dioxide.  Tn  other  cases,  the 
original  ores  are  changed  through  the  action  of  air  into  soluble 
substances  which  then  escape  downstream.  Sulphide  ores  are 
thus  oxidized  in  the  presence  of  air  into  soluble  copper  sulphate. 
Inasmuch  as  il  is  well  known  thai  minute  amounts  of  copper  in 
solution  are  extremely  toxic  to  plant  roots  directly  exposed  to 
them,  some  apprehension  naturally  existed  as  to  the  effects  of 
these  small  amounts  of  copper  salts  escaping  into  1  he  water- 
supply  of  an  irrigated  district. 

Tn  some  respects,  conditions  were  especially  favorable  here 
to  the  successful  prosecution  of  a  stud}  of  the  foregoing  ques 
tion.  The  irrigated  lands  are  at  a  distance  of  twenty  miles  or 
more  from  the  smelters,  so  thai  injurious  eases  could  not  cum 
plicate  effects  upon  irrigated  crops,  There  are.  also,  only  traces 
of  other  toxic  metals  to  be  found  within  the  district. — more  par- 
ticularly, arsenic,  antimony,  and  zinc.  Injurious  effects  due  to 
the  possible  toxic  action  of  compounds  originating  in  the  mines 
are  therefore  limited  to  copper. 

Scientific  study  relating  to  toxic  effects  of  copper  upon  plaids 
under  varying  conditions  has  thoroughly  established  not  only 
the  fact  that  copper  compounds  are  extremely  toxic  to  plants 
when   they  obtain   entry  to  their  tissues,   but    also   that    various 


400      University  of  California  Publications  in  Agricultural  Sciences    [Vol.  1 

agencies  standing  between  these  poisonous  salts  and  the  living 
plant  tend  to  prevent  injury.1  Soluble  copper  compounds,  for 
instance,  react  with  carbonate  of  lime,  commonly  abundant  in 
soils  of  the  arid  region,  to  form  the  solid  carbonates  of  copper. 
The  partly  decomposed  silicates  of  these  soils  also  precipitate 
soluble  compounds  of  copper  and  mask  their  toxic  character. 
Organic  matter  in  the  soil  likewise  holds  large  quantities  of 
copper  in  comparatively  harmless  combinations.  Through  physi- 
cal attraction  or  adsorption,  soluble  copper  compounds  enter  into 
weak  combination  with  fine  soil  particles  and  toxic  effects  are 
thereby  greatly  lessened.  In  the  presence,  also,  of  other  soluble 
salts,  such  as  the  various  forms  of  "alkali"  commonly  found  in 
the  soils  of  the  region,  the  toxicity  of  copper  compounds  is  enor- 
mously lessened. 

The  investigations  recorded  in  this  publication  include:  (1) 
Observations  upon  the  distribution  of  copper  in  mining  wastes, 
in  irrigating  waters,  in  soils  and  soil  waters,  in  the  plants,  and 
in  the  animal  life  of  the  region.  (2)  The  development  of  accu- 
rate methods  for  the  determination  of  minute  amounts  of  copper 
in  all  situations  where  they  may  occur.  (3)  Plant  cultural 
work  with  waters  and  in  soils  in  the  presence  of  varying  propor- 
tions of  copper  and  under  varying  conditions.  (4)  A  careful 
analytical  study  of  the  results  of  such  cultures  in  order  to  deter- 
mine the  symptoms  of  poisoning  and  the  distribution  of  copper 
throughout  poisoned  plants ;  and  to  identify,  if  possible,  the 
particular  parts  of  plants  and  tissues  injured  by  copper.  (5) 
A  physiological  study  of  plant  reactions  with  copper.  (6)  Field 
studies  for  the  purpose  of  relating  the  results  of  laboratory  inves- 
tigations to  the  question  of  economic  injury  done  by  copper  salts 
to  irrigated  crops. 

By  reason  of  interruptions  due  to  other  duties,  it  has  required 
a  long  time  to  mature  this  investigation  to  the  point  where  it 
seems  sufficiently  complete  for  publication.  This  delay,  however, 
has  given  perspective  to  the  work  and,  especially,  opportunity  to 
verify  earlier  conclusions  as  applied  to  field  conditions. 

The  writer  is  indebted  for  painstaking  analytical  work  to 
Messrs.   R.   G.   Mead,   Edward   E.   Free,   Dr.   W.   H.   Ross   and 


i  See  Bibliography,  pp.  487-488,  references  1,  8,  14,  15,  16,  19,  34,  51. 


J917]     Forbes:  Irrigation  Effects  of  Copper  Compounds  Upon  Crops       mi 

C.  X.  Catlin,  associated  with  the  Arizona  Agricultural  Experi 
Minit  Station  from  time  to  time;  and  to  the  helpful  advice  of 
Dr.  Howard  S.  Reed,  of  the  Universitj  of  California  Graduate 
Scl 1  of  Tropica]  Agriculture,  in  connection  with  the  physio- 
logical pari  of  the  work  herein  described.  The  publication,  also, 
lias  been  criticized  to  its  advantage  by  Dr.  ('.  B.  Lipman  of  the 
I  fniversil  y  of  ( Jalifornia. 


DISTRIBUTION   OF    COPPEB    COMPOUNDS    THROUGH- 
OUT THE  CLIFTON-MORENCl  AND  GILA  RIVKI; 
MINING  AND  IRRIGATION  DISTRICTS 

Sources  of  Copper 

The  original  smiivc  of  flic  copper  found  in  this  district, 
according  to  Lindgren,2  is  a  Cretaceous  or  early  Tertiary  in- 
trusion of  acidic  porphyries  to  which,  in  the  Clifton-Morenci 
district,  all  ore  deposits  may  be  finally  referred.  The  original 
porphyries  contain  as  little  as  0.02  per  cent  of  copper  ore  m 
the  form  of  chalcopyrite.  Under  the  influence  of  superheated 
waters  emanating  from  the  porphyry,  this  chalcopyrite,  together 
with  other  metallic  compounds,  was  carried  out  from  the  molten 
intrusive  mass  into  adjoining  strata  and  there  deposited,  espe 
cially  along  fissures,  in  the  form  of  concentrated  masses  or  veins 
of  chalcopyrite  and  other  minerals.  Through  erosion  these  de 
posils  were  afterward  subjected  to  atmospheric  oxidation,  fol- 
lowed by  downward  percolation  and  a  period  of  secondary  enrich- 
ment due  to  numerous  reactions  mainly  between  the  oxidized 
compounds  of  copper  and  other  minerals  present. 

In    limestones    and    shales,    these    processes    resulted    in    the 
formation  of  oxidized  ores  containing  azurite,  malachite,  chryso 
colla,    and    cuprite.       In    porphyry,    the    main    final    result    was 
chalcocite  or  copperglance,  the  principal  constituent  of  the  sul- 
phide ores  of  the  Clifton-Morenci  district. 

In  general,  therefore,  the  metasomatic  changes  associated, 
first,  with  superheated  waters  arising  from  the  original  intrusion 
of  molten  porphyry  and.  second,  with  meteoric  waters  percolating 


'-'  V.  S.  Geological  Survey,  Professional   Paper  No.  43,  1005. 


402      University  of  California  Publications  in  Agricultural  Sciences    [Vol.  1 

downward  with  oxidiziug  effects  through  copper-bearing  rocks, 
have  brought  copper  from  a  concentration  of  possibly  less  than 
0.02  per  cent  in  the  original  porphyry  through  every  degree  of 
richness  to  the  condition  in  some  cases  of  pure  copper. 


Processes  by  which  Copper  is  Added  to  the  Water-Supply 

To  a  slight  extent,  drainage  waters  from  the  ore  deposits  and 
from  the  mines,  containing  considerable  amounts  of  copper  in 
solution,  find  their  way  downstream.  But  by  far  the  larger  part 
of  the  copper  which  gets  into  the  irrigating  supply  is  derived 
from  the  ores  and  tailings  which,  in  the  concentrators,  on  the 
dumps,  and  finally  in  the  river  itself,  are  subjected  to  the  action 
of  atmospheric  oxygen,  and  water  containing  carbon  dioxide  and 
various  salts  in  solution.  The  residual  chalcocite  in  tailings  from 
sulphide  ores  thus  reacts  with  oxygen  from  the  air  and  yields 
copper  sulphate  in  solution.  This,  in  turn,  reacts  with  the  excess 
of  bicarbonate  of  lime  ordinarily  contained  in  the  waters  of  the 
San  Francisco  and  Gila  rivers.  The  resulting  basic  carbonate  of 
copper  is  notably  soluble  in  water  containing  carbon  dioxide  and 
certain  of  the  various  salts  commonly  found  in  river  waters.  The 
residues  of  carbonates  of  copper  in  oxidized  ores  are  directly 
dissolved  in  waters  containing  carbon  dioxide  and  certain  soluble 
salts. 

Along  with  minute  quantities  of  copper  thus  dissolved  and 
carried  forward,  pass  the  solid  residues  discharged  from  the 
concentrators — solid  wastes  which  find  their  way.  unchanged, 
downstream  and  finally  upon  the  soils  of  irrigated  fields.  At  this 
point  begins  another  and  very  important  series  of  reactions  be- 
tween dissolved  copper  compounds  and  the  soil,  tending  in 
general  to  withdraw  copper  from  its  solutions  and  precipitate 
it  in  the  form  of  less  harmful  solid  compounds.  These  are  briefly 
referred  to  above  and  will  be  discussed  more  in  detail  further 
on  in  this  paper.  Opposing  these  precipitations  of  copper 
are  those  solvents  which  tend  to  maintain  this  metal  in  soluble 
form  in  small  quantities  in  the  soil.  Chief  of  these  is  carbon 
dioxide,  which  is  always  present  in  agricultural  soils  in 
significant  quantities.     Of  interest  in  this  connection  is  the  fol- 


r.M,       Forbes:  Irrigation  Effects  of  Copper  Compounds  Upon  Crops      403 


TABLE  r 
Solubilities  of  Copper  <  ompounds 


Compound 

Malachite 
CuCO,.Cu(OH)3 

Precipitated  basic 
copper  carbonate 

Precipitated  basic 
copper  carbonal  e 

Precipitated  basic 
copper  carbonate 

Precipitated  basic 
copper  carbonate 

Precipitated  basic 
copper  carbonate 

Precipitated  basic 
copper  carbonate 

Precipitated  basic 
copper  carbonate 

Precipitated  basic 
copper  carbonate 

Precipitated  basic 
copper  carbonate 

Precipitated  ba   ic 
copper  carbonate 

<  'opper  sulphide; 

CuS 
( !halcopyrite 
CuFeS3 

Chalcopyrite 
CuFeS 

Malachite 


Chrysocolla 
di  SiO,.n  H\0 

Cupric  sulphide 

CuS 
<  uprite 
Cu,0 
( lupric  oxide 
CuO 


Solvent 

Water  containing  0.12*  < 
carbon   dioxide 

I'u  re    water 


Water  containing  ti.li"; 
carbon   dioxide 

Water  containing  0.13% 
c  a  r  b  o  n  dioxide  and 
0.0195     sodium    chloride 

Water  containing  0.13% 
c  a  r  b  o  n  dioxide  and 
1.0%    sodium    chloride 

\\  ater  i  ontaining  o.l  i" ", 
c  a  r  h  O  ii  dioxide  a  nd 
0.01%   sodium   sulphate 

Water  containing  0.12% 
c  a  r  Ii  o  ii  dioxide  and 
I   "'  ,     sodium     sulphate 

w  ater  containing  0.12% 
carbon  dioxide  and 
0.01%  sod.  carbonate 

Water  containing  0.12% 
c  a  r  li  ii  n  dioxide  and 
l.ie ;   sod.  carbonate 

Water  containing  0.129$ 

C  a  r  Ii  ii  a     dioxide    and 

I    calcium   sulphate 

Water  containing   0.129? 

C  a  r  b  (i  ii     dioxide    and 

0.11%   cale.  carbonate 
Oxygen  free  water 


Cu  dissolved 

parts  pel 

million 


Reference 

E.  E.  Free,  Journ. 

29.0  31.0     Am.    Chem.    Soc  . 

XXX,   9,   p.    1367 

1.5       E.  E.   Free,  Journ. 

Am.     Chem.     Sue.. 
XXX.    9,     p.     1370 

E.   E.   Free,  Journ. 

34.8         Am.    Chem.    Soc, 

XXX,   9,    p.    L370 

E.  E.  Free,  Journ. 

Am.    Chem.    Soc, 

36.0  XXX,    9,    p.    1371 

B.   E.   Free,  Journ. 

Am.    Chem.    Soc, 

58.0         XXX.   9,   p.    1371 

E.   E.  Free,  Journ. 

Am.     Chem.    Sue.. 

37.il  XXX,    9,    p.    1372 

E.    E.    Free,  Journ. 

Am.     Chem.    Soc. 

.18.0         XXX,   9,    p.   1372 

E.   E.   Free,  Journ. 

Am.     Chem.     Soc, 

10.0         XXX.   9,   p.    1372 

E.   E.  Free,  Journ. 

Am.     Chem.     Sue.. 

0.7         XXX,   9,   p.    L372 
E.   E.   Free,  Journ, 

Am.     Chem.     Soc, 

36.0         XXX.   9,   p.    L372 

E.  E.  Free,  Journ. 

Am.    ('hem.    Soc, 

It  XXX.    9,    p.    1372 

0.09     W.   H.    Ross,   MSS 


I'u  re  water 


SodiC     sulphide 


measurable 

amounts 

Amt.  not 
stated 


'  '  insoluble  in  water,  slightly 
soluble  in  water  charged 
with    carbon    dioxide.'' 

"Somewhat  soluble  in  water 
with  carbon  dioxide 

u  ater  1  to  950,000 

"Insoluble   in    water" 

"  [nsoluble   in   water 


F.  S.  Geol.  Survey 

Monograph 

XLVII,  p.  1107 
r.  S.  •  leol.  Survey 

Monograph 

\  LVII,  p.  1106 
Moissan    5,    p.    1 1>7 


Lindgren,    U.   S. 
u    S.   Prof,  paper 
13,  p.   188 

Comey,  1  >ict.  Solu 
bilities,  p.  139 

Comey,  Diet.  Solu- 
bilities, p.   137 

Comey,  Diet.  Solu- 
bilities, p,   l.",7 


406      University  of  California  Publications  in  Agricultural  Sciences    [Vol.  1 


s 

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a 


to 


1917]     Forbes:  Irrigation  Effects  of  Copper  Compounds  Upon  Crops       407 

in  low-grade  sulphide  ores  (No.  3491,  No.  3303),  and  to  nearly 
one-half  in  the  richer  oxidized  ores  (No.  3492,  No.  3304,  No. 
3439).  By  far  the  larger  portion  of  tailings  produced,  however, 
are  from  low-grade  sulphide  ores,  the  wastes  from  which  there- 
fore predominate,  formerly  imparting  to  river  waters  the  whitish 


TABLE  III 

Dissolved  Copper  in  River,  Irrigating,  and  Ground  Waters  below  the 


Sample  No. 
and  date 

3438 
June  28,  '05 

3439 
June  28, '05 

3309 
May  26,  '04 

3486 
June  11, '05 

3622 
June  25,  '06 

3737 
Feb.  22, '07 

Tailings 

4011 
Jan.     3,  '09 

4029 
Apr.  12 

6342 
Mar.    4, 

3986 
Jan.     2,  '09 

Records  of 
Cananea 
C.  C.  Co. 
Jan.     4, '14 

3504 
Aug.  19, '05 

4012 
Jan.     3, '09 

3526 


09 


16 


Clifton-Morenci  District 


Description  of  sample 
Water  mixed  with  sulphide  tailings 

from  A.  C.  Co.  's  mill,  Clifton 
Water  mixed  with  oxidized  tailings 

from  A.  C.  Co.  's  mill,  Clifton 
Montezuma   Canal   water   at   Solo 

monville;  slight  rise  in  river 
Montezuma  Canal  at  Solomonville 

small  flood 
Montezuma  Canal  at  Solomonville 

head  waters  clear 
Montezuma  Canal  at  Solomonville, 

medium  flood 

shut  out  of  water  supply  May  1,  1908 
Water   from   Montezuma   Canal   at 

Solomonville 
Montezuma  Canal  at  Solomonville 

Montezuma  Canal  at  Solomonville 
high  water 

Water  from  C.  &  A.  Ditch,  Bisbee 
mine  waters 


Water  from  creek  below  concen- 
trator 

Water  from  Geo.  Olney's  well,  30  ft. 
deep,  east  of  Safford,  under 
Montezuma  Canal  7000 

Water  from  Wilson  's  well,  one-half 
mile  west  of  Solomonville  under 
San  Jose  Canal  3500 

Water    from   University   well,    Tuc- 
son, 95  ft.  deep,  tapping  Rillito 
underflow  7000 


Condition  and 
amount  taken 
in  cc. 

Cu 

found, 
grains 

Cu 
p.p.m 

500 

.0009 

1.80 

500 

.0018 

3.60 

2000 

.0016 

.80 

6000 

.0015 

.25 

9000 

.00095 

.11 

14000 
1908. 

.0403 

2.88 

4000 

.00031 

.08 

!    3700 

.0003 

.08 

1000 

.00003 

.03 

3500 

.00039 

.11 

.0037 
less 
than 

.00001 


none 


2.1 


.53 
less 
than 
.00?. 


none 


appearance  characteristic  of  this  material.  It  is  of  interest  to 
note  in  this  connection  that  in  one  instance  observed  the  tailings 
almost  completely  maintained  their  richness  in  copper  between 


408      University  of  California  Publications  in  Agricultural  Sciences    [Vol.  1 

Clifton  and  Solomonville.  At  Clifton,  May  23,  1904,  the  prin- 
cipal discharge  of  sulphide  tailings  (3303)  was  observed  carrying 
0.93  per  cent  of  copper.  At  Solomonville,  three  days  later,  the 
Montezuma  ditch-water  sediments  (No.  3309),  mostly  of  this 
same  material,  carried  0.86  per  cent  of  copper,  indicating  the 
persistence  with  which  the  copper  accompanies  the  wastes,  with 
which  it  is  associated,  downstream  and  upon  underlying  irrigated 
lands. 


TABLE  IV 
Copper  in  Soils  Irrigated  with  Tailings  Waters 


Sample  No. 
and  date 

3435 
May  25, '04 


3434 
June  10, '05 

350] 

Aug.  19,  '05 

3436 
June  25, '05 


3437 

June  25, '05 

3502 
Aug.  19, '05 

2381 
June    5, '00 

3522 
Oct.   25, '05 


3521 
Oct.  25/05 

2763 
Nov.  11, '01 

1.S9U 
Apr.  20, '01 

2830 
Jan.  19, '00 


Description  of  sample 

Top  5  in.  sedimentary  soil  (Fred 
Thorstison),  upper  end  alfalfa 
field  west  of  Safford,  under 
Montezuma  Canal 

Top  5  in.  sedimentary  soil  (Geo. 
Olney),  upper  end  alfalfa  field 
east  of  Safford,  under  Monte- 
zuma   Canal 

Soil  in  place  at  4  ft.  depth  beneath 
No.  3434 

Top  sedimentary  soil  (Wm.  Gilles- 
pie), upper  end  of  test  alfalfa 
field  west  of  Solomonville,  under 
Montezuma  Canal 

Soil  in  place,  no  sediments  at  sur- 
face of  lower  end  of  field  near 
No.  3436 

Soil  in  place  at  4  ft.  depth  beneath 
No.  3437 


Condition  and 

weight  taken, 

grams 


12    in.    from    garden    near 
Ariz.,  beyond  tailings  de- 


Surface 
Pima, 
posits 

Top  4  in.  sedimentary  soil  upper 
end  of  alfalfa  field,  Station  farm 
near  Phoenix,  under  Grand  and 
Maricopa  canals 

Deep  soil,  no  sediments,  Station 
farm  near  No.  3522 

Surface  12  in.  from  orange  orchard 
north  of  Phoenix,  under  Ari- 
zona Canal 

Surface  15  in.  from  cultivated  field 
west  of  Tempe,  under  Tempe 
Canal 

Surface  12  in.  from  orange  orchard 
northeast  of  Phoenix,  under  Ari- 
zona Canal 


Cu 
found,  Cu 

grams  p. p.m. 


96.7 
water-free 


96.s 
water-free 

96.2 
water-free 


96.7 
water-free 

94 
water-free 

96.1 
water-free 

100 
air-dry 


95 
water-free 

95 
water-free 

100 
air-dry 

100 
air-dry 

100 
air-dry 


.020 

.0199 
.0021 

.0192 

.0028 
.001 


faint 
trace 


207 

205 

22 

199 

30 
10 


faint 

trace        trace 


.0003  3 

.0003  3 

faint 

trace  trace 


trace 


1917]     Forbes:  Irrigation  Effects  of  Copper  Compounds  Upon  Crops       409 

Table  III  is  of  interest  because  it  reveals  quantities  of 
dissolved  copper  in  irrigating  and  in  ground  waters  sufficient, 
under  proper  conditions,  in  water  cultures,  to  produce  toxic 
effects  upon  plants.4  It  is  noteworthy,  however,  that,  following 
the  order  of  the  court,  effective  May  1,  1908,  prohibiting  the  in- 
troduction of  tailings  into  the  water-supply,  the  amount  of  dis- 
solved copper  in  Montezuma  canal  waters  greatly  decreased,  due 
to  the  decrease  in  quantity  of  sulphides  whose  oxidation  affords 
the  supply  of  dissolved  copper.  Other  water-supplies  also  are 
found  to  contain  similar  amounts  of  copper,  as  the  Calumet  and 
Arizona  mine  waters,  used  for  irrigation  below  Bisbee.  As  stated 
above,  however,  in  the  soil  itself  the  toxic  action  of  such  copper 
solutions  is  enormously  decreased.  Naturally,  the  question  arises 
as  to  the  possibility  of  toxic  effects  in  using  such  waters  upon 
cultivated  soils.  This  is  discussed  on  subsequent  pages.  The 
proportions  of  copper  (0.003  to  0.53  parts  in  1,000,000  of  water) 
found  in  the  drainage  beneath  this  irrigated  district  indicate 
that  not  all  of  the  copper  applied  in  irrigation  remains  in  the  soil. 
University  well  water  at  Tucson  was  observed  to  be  free  from 
this  element. 

Soils  Nos.  3435,  343-4,  and  3436  show  maximum  amounts  of 
copper,  inasmuch  as  they  are  composed  to  a  considerable  extent 
of  tailings.  The  soils  in  place  beneath  these  sediments,  Nos.  3501 
and  3502,  contain  much  less,  yet  noticeable  amounts  of  copper, 
most  of  which  is  retained  where  it  first  comes  in  contact  with 
the  top  soil.  It  is  of  interest  to  note  that  the  surface  sediments 
and  the  deep  soils  of  the  Experiment  Station  farm  near  Phoenix, 
Arizona,  irrigated  from  an  entirely  different  watershed,  also  con- 
tain small  but  weighable  amounts  of  copper.  This  was  probably 
derived  from  mines  at  Globe  and  Jerome,  Arizona,  whose  wastes 
have  found  their  way  into  the  drainage  which  supplies  irrigation 
for  Salt  River  Valley.  The  quantities  observed,  however,  three 
parts  copper  per  million  of  soil,  are  negligible.  Other  soils  from 
Salt  River  Valley  also  show  traces  of  copper. 


i  See  Bibliography,  p.  487,  references  5,  18. 


410      V niversity  of  California  Publications  in  Agricultural  Sciences    [Vol.  1 

TABLE  V 

Miscellaneous  Soils  Unaffected  by  Mining  Detritus 

Condition  and         Cu 
Sample  No.  weight  taken,       found,  Cu 

and  date  Description  of  sample  grams  grams         p. p.m. 

2375         Surface    12   in.    from    new   ground 
June    5,  '00       near     Safford,     recently     placed         100 

under   Montezuma   Ditch  air-dry  none         none 

2253         Surface   12   in.   university   ground,  100 

Jan.     3, '00       Tucson  air-dry          none         none 

3503  Surface    12    in.    virgin    unirrigated 

May    9, '05       soil,  Colorado  Valley  bottom  near  100 

Yuma  air-dry          none         none 

These  determinations,  made  in  widely  separated  localities, 
indicate  the  absence  of  copper  in  soils  which  are  not  immediately 
under  the  influence  of  mining  detritus. 


TABLE  VI 

Copper  in  Vegetation  from  Upper  Gila  Valley  Farms 


Sample  No. 
and  date  Description  of  sample 

3505  Alfalfa,     before     blooming,     from 

Aug.  19, '05       upper  end  of  Geo.  Olney's  field 
east    of    Safford,    under    Monte- 
zuma Ditch 
3512         Alfalfa  from   bale  grown   in   Lay 
Aug.  19, '05       ton  (M.  B.  Steele)  under  Monte- 
zuma ditch 
3507         Corn  in  bloom,  leaves  only,  grown 
Aug.  20, '05       in  Layton   (Jas.  Welker),  under 
Montezuma  Ditch 
3509         Wheat  from  stack,  stalk  and  grain, 
Aug.  19, '05       grown  in  Layton  (M.  B.  Steele), 
under  Montezuma  Ditch 
.'..">  1.".         Mistletoe,  growing  on  willow  25  ft. 
Sept.  19,  '05       above  ground,  one  mile  east  of 
Safford,  under  Montezuma  Ditch 

3739  Alfalfa  seed,  crop  of  1906,  grown 

near  Pima  under  Smithville  Ditch 
3741  Alfalfa  seed  (Wm.  Gillespie),  crop 

of  1906,  grown  near  Solomonville, 

under  Montezuma  Ditch 
3780         Shelled  corn,  crop  of  1906,  grown 

at    Solomonville,    under    Monte 

zuma  Ditch 

3740  Shelled  corn,  crop  of  1906,  grown 

at    Solomonville,    under    Monte 
zuma  Ditch 
3738         Shelled  corn,  crop  of  1906,  grown 
near     Pima,     under     Smithville 
Ditch 


Condition  and 

weight  taken, 

grams 

i 

Cu 

found, 
grams 

Cu 
p.p.m. 

[ 

1206 
air-dry 

.0062 

5.10 

1 359 
air-dry 

.0077 

5.70 

i 

545 
air-dry 

.0033 

6.10 

]       1125 
air-dry 

.0027 

2.40 

!       1245 
air-dry 

.0094 

7.60 

l         782 
water-free 

.0026 

3.33 

> 

,         843 
water-free 

.0023 

o  -o 

i 

932 
water-free 

.0004 

.43 

i 

874 
water-free 

.0008 

.73 

L 

i       1092 
water-free 

trace 

trace 

1917]     Forbes:  Irrigation  Effects  of  Copper  Compounds  Upon  Crops       411 

The  prevalence  of  small  amounts  of  copper  in  vegetation 
throughout  this  locality  is  shown  by  the  figures  in  table  VI. 
Samples  of  corn  and  alfalfa  contained  comparable  quantities  of 
copper,  which,  however,  were  exceeded  by  the  amount  found  in  a 
sample  of  mistletoe  growing  on  a  willow  fully  twenty-five  feet 
above  the  ground.  This  is  due  chiefly  to  the  perennial  character 
of  mistletoe  which,  therefore,  has  more  time  to  accumulate  cop- 
per. It  is  interesting  to  note  also  that  seeds  of  alfalfa  and 
corn  contain  less  copper  than  corresponding  foliage.  Corn  leaves 
were  observed  to  contain  6.1  parts  of  copper  per  million  parts  of 
air-dry  substance,  while  grain  from  the  same  locality  contained 
from  0.73  to  0.43  parts.  Alfalfa  seed  contained  about  one-half 
as  much  copper  as  the  stalks  and  leaves,  while  wheat  hay  carry- 
ing a  large  proportion  of  grain  showed  a  low  proportion  of  cop- 
per.     These   facts  are   probably   connected   with   transpiration, 

TABLE  VII 
Copper  in  Vegetation  from  Other  Localities 

Sample  No. 
and  date  Description  of  sample 

3508         Alfalfa    hay,    station    farm    near 
Aug.  25, '05       Phoenix   (two  samples) 

3516  Alfalfa,    before    blooming,    station 
Oct.  25,  '05       farm  near  Phoenix 

3515  Alfalfa     hay,      Colorado      bottom, 

Oct.     4, '05  Yuma  date  orchard 

3517  Barley     hay,     station     farm     near 
May,    1905  Phoenix  " 

3518  Corn,  leaves  only,  station  farm  near 
Oct.  25, '05  Phoenix 

3519  Corn,  leaves  only,  grown  on  Rillito 
Oct.  14, '05  near  old  Fort  Lowell 

3529         Corn,  leaves  and  bloom,  same  field 
Dec.  27, '05       as  No.  3519 

3520  Mistletoe   from   cottonwood   30   ft. 
Oct.  14,  '05       above  ground,   old  Fort   Lowell, 

near  Tucson 

3989  Young    (5   mos.   old)    alfalfa   roots 
Dec.  31, '08       from    C.    &    A.    ranch    irrigated 

with  mine  waters  containing  cop- 
per, from  Bisbee 

3990  Corn  roots  from  C.  &  A.  ranch  irri- 

gated with  mine  waters  contain- 
ing copper,  from  Bisbee 


Condition  and 

weight  taken, 

grams 

2109 
air-dry 

1408 
air-dry 

Cu 
found, 
grams 

.0021 

.0031 

Cu 
p.p.m. 

1.00 

2.20 

1106 
air-dry 

.0011 

1.00 

1262 

air-dry 

none 

none 

1304 
air-dry 

.0002 

.15 

595 
air-dry 

.0005 

.84 

284 
air-dry 

.0018 

6.30 

1132 
air-dry 

.0015 

1.32 

1160 
air-dry 

.001 

.85 

2.12 
air-dry 

.0001 

47.00 

16.7 
air-dry 

.00025 

15.00 

412      University  of  California  Publications  in  Agricultural  Sciences    [Vol.  1 

which  is  maximum  in  leaves  and  quantitatively  small  in  the 
fruiting  parts  of  a  plant.  Additional  evidence  of  this  fact  is 
shown  in  poisoned  corn  plants,  which  are  discussed  on  a  subse- 
quent page. 

Comparing  the  data  of  table  VII  with  those  of  table  VI.  it  is 
evident  that,  excluding  corn  and  alfalfa  irrigated  with  C.  &  A. 
mine  waters,  in  every  case  except  that  of  one  sample  of  corn  from 
old  Fort  Lowell  (No.  3519)  the  copper  in  crops  grown  on  Gila 
Valley  farms  is  much  in  excess  of  that  in  plants  coming  from 
elsewhere  for  the  same  classes  of  material.  The  presence  of 
appreciable  amounts  of  copper  in  samples  of  alfalfa,  corn,  barley, 
and  mistletoe  also  accords  with  the  fact  that  the  soils  in  which 
they  were  grown  receive  the  drainage  from  copper-bearing  water- 
sheds. The  one  exception,  at  Yuma  (No.  3515)  where  qo  trace 
of  copper  could  be  found  either  in  alfalfa  or  in  soil  (No.  .'5503). 
indicates  that  these  alluvial  river  deposits,  which  have  been  sub- 
jected annually  to  the  leaching  action  of  enormous  quantities  of 
Hood  waters,  liave  been  prevented  from  accumulating  appreciable 
quantities  of  copper. 

Copper  in  the  Flesh  and  Bones  <>f  a  Pig 

In  order  to  follow  the  copper  as  Ear  as  possible  in  its  trans- 
migrations, a  five-months-old  pig  that  had  been  born  and  brought 
up  in  an  alfalfa  pasture  near  Solomonville  under  the  Montezuma 
Ditch,  was  killed  and  portions  of  the  Hesh  and  hones  were  taken 
for  examination,  with  the  following  results: 

Condition  and        Cu 
Sample  No.  weight  taken,      found.  Cu 

and  d.i  I  ■■  Description  of  sample  grams  grams  p. p.m. 

3779  917 

May    7, '07  Liver,  heart,  and  rib  moat  fresh         .0053  5.78 

3778  998 

May     7, '07  Ribs  and   rib   meat  fresh         .00006  .0(5 

The  largest  amount  of  copper  was  found  in  portions  of  liver. 
heart  and  rib  meat,  only  minute  amounts  being  present  in  the 
bony  material.  In  this  connection,  it  is  stated  that  about  two 
parts  of  copper  have  been  observed  in  one  million  parts  of  human 
liver;  ten  parts  in  human  kidneys,  and  as  much  as  fifty  parts 


1917  I     Forbes:  Irrigation  Effects  of  tapper  Compounds  Upon  Crops       413 

in  sheep's  liver.5  Human  food,  however,  is  commonly  contam- 
inated with  copper  compounds,  which  account  for  its  presence 
in  the  human  body. 

///  brief,  the  observations  detailed  above  have  shown  the  suc- 
cessive positions  of  copper  in  the  original  ores  of  the  Clifton- 
Morenci  district;  in  the  tailings  wastes  from  these  ores,  in  sus- 
pension and  in  solution  in  river  waters  exposed  to  milling 
operations ;  in  soils  irrigated  with  these  waters ;  in  the  ground 
waters  beneath  these  soils ;  in  vegetation  growing  upon  them ; 
and  even  in  the  animal  life  of  the  region.  It  is  of  interest  to  ob- 
serve, first,  the  concentration  through  natural  processes  of  small 
amounts  of  copper  in  the  original  rocks  into  the  form  of  rich 
ores ;  and,  second,  the  reversal,  through  human  agencies,  of  this 
process,  and  the  dilution  of  copper  values  till,  in  vegetation  and 
in  animal  life,  but  traces  of  the  metal  can  be  detected. 


DISTRIBUTION  OF  COPPER  IN  PLANTS  WITH  ROOT 
SYSTEMS  EXPOSED  TO  COPPER  COMPOUNDS 

Corn  Plants  Grown  in  Soils  Containing  Copper 
In  order  to  determine  accurately  the  distribution  of  copper 
throughout  a  typical  crop  plant,  thereby  locating  if  possible  the 
points  at  which  injury  may  occur  from  copper  compounds  in  the 
soil,  three  lots  of  corn  plants  were  examined  in  detail.  Two  of 
these  were  grown  (August  3  to  November  13,  1907)  in  pots  con- 
taining thirty-eight  pounds  of  sandy  loam  soil  very  thoroughly 
mixed  with  0.01  and  0.025  per  cent  of  copper  in  the  form  of 
freshly  precipitated  copper  carbonate  (Cu(OH)._,.CuC03),  made 
by  mixing  equivalent  amounts  of  copper  sulphate  and  sodium 
carbonate.  The  third  was  grown  in  soil  containing  0.05  per  cent 
of  copper  in  the  form  of  finely  pulverized  chalcocite. 

The  samples  were  harvested  with  care  to  prevent  contamina- 
tion with  copper  dust ;  the  root  portions  being  washed  in  copper- 
free  water  saturated  with  carbon  dioxide  until  the  washings 
contained   no   trace   of  copper.     Determinations   of   copper,   as 


Blyth,  Poisons,  fourth  edition,  pp.  640-641. 


414      University  of  California  Publications  in  Agricultural  Sciences    [Vol.  1 

usual,  were  made  as  shown  under  "Methods  of  Analysis"  (see 
Appendix  herewith).     Following  are  the  tabulated  results: 

TABLE  VIII 


Eleven  Stalks  of  Corn  Grown  in  Soil 

Containing 

0.01    PER 

CENT 

Copper  as  Cu(OH)2.CuC03  (1907) 

No. 
3869p 

Plant  part 
Lower   six    nodes,    24    in.    long 

Weight 

of  sample, 

grams 

43.4 

Cu  found, 
grams 

.00012 

Cu 
p. p.m. 

3.00 

3869<z 

Basal  sheaths   of  leaves  from  lower 
six  nodes 

23.2 

.0001 

4.00 

3869r 

Blades  of  leaves  from  lower  six  nodes 

33.1 

.00029 

9.00 

3869s 

Upper  four-seven  nodes,  24  in.  long 

24.2 

.00017 

7.00 

3869« 

Basal   sheaths   of   leaves  from   upper 
nodes 

20.6 

.00013 

6.00 

3869m 

Blades  of  leaves  from  upper  nodes 

19.6 

.00024 

12.00 

3869d 

Rudimentary  ears 
Whole  top  portions 

11.8 

.0001 

9.00 

3869 

175.9 

.00115 

6.50 

3868 

Roots 

10.6 

.00161 

152.00 

TABLE  IX 

Ten  Stalks  of  Corn  Grown  in  Soil  Containing  0.025  Per  Cent 
Copper  as  Cu(OH)2.CuC03  (1907) 


No.  Plant  part 

3865a     Five  lower  nodes,   14.4  in.  long 

3865b     Basal   12  in.   of  leaves  and   sheaths 
from  five  lower  nodes 

3865c     Terminal  14  in.  of  leaves  from  five 
lower  nodes 

3865a"     Upper  five-seven  nodes,  14  in.  long, 
including  tassels  and  ears 

3865e     Leaves  from  same 


3865  Whole  top  portions 

3866  Roots 


Weight 

of  sample, 

grams 

17 

Cu  found, 
grams 

.00024 

Cu 
p.p.m. 

14.00 

17.2 

.00037 

22.00 

14.4 

.00047 

33.00 

9.2 

.00017 

19.00 

19.2 

.00035 

18.00 

77 

.0016 

21 

9.2 

.0067 

728 

1917]     Forbes:  Irrigation  Effects  of  Copper  Compounds  Upon  Crops       415 

TABLE   X 

Four  Stalks  op  Corn  Grown  in  Soil  Containing  0.05  Per  Cent 
Copper  as  Cu2S.     (1908) 


No. 
3968p 

0 

Plant  part 
Lower  six  nodes 

Weight 
f  sample, 
grains 

11.5 

Cu  found, 
grams 

.00010 

Cu 

p.p.m. 

9.00 

3968g 

Basal  sheaths  from  lower  six  nodes 

7.5 

.00008 

11.00 

3968r 

Blades  from  do. 

15.7 

.00021 

13.00 

3968s 

Upper  five-six  nodes 

3.5 

.00004 

11.00 

3968* 

Basal  sheaths  from  upper  five-six  nodes 

5.2 

.00007 

13.00 

3968m 

Blades  from  do. 

4.9 

.00010 

20.00 

3968v 

Rudimentary  ears 
Whole  top  portions 

3.4 

.00005 

15.00 

51.7 

.00065 

12.50 

3978a 

Fine  roots 

3.23 

.00081 

251.00 

39785 

Coarse  roots 

2.91 

.00024 

83.00 

whole  root  system  6.14  .00105  171.00 

In  all  of  the  corn  samples  shown  above,  the  copper  content 
of  root  systems  is  very  much  greater  than  that  in  the  top  por- 
tions of  the  plants,  amounting  to  twenty-three  times,  thirty-four 
times,  and  thirteen  times  as  much,  respectively.  In  the  aerial 
parts  of  all  samples  copper  increases  slightly  but  uniformly  to- 
wards the  upper  and  outer  portions  of  the  plants.  This  must 
be  an  effect  of  transpiration,  by  which  copper  in  solution  is 
carried  to  the  terminal  portions  of  the  plant  and  there  deposited. 
The  fine  roots  of  one  sample  were  found  to  contain  about  three 
times  as  much  copper  as  the  coarse  roots — a  fact  which  can  be 
explained  by  the  greater  proportion  of  absorbing  surface  to 
weight  in  small  roots. 

With  reference  to  toxic  effects,  the  culture  in  0.01  per  cent 
copper  carbonate  showed  only  a  faint  yellow  striping  of  leaves, 
with  no  checking  of  growth.  The  0.025  per  cent  culture  gave 
leaves  which  were  strongly  striped  with  yellow,  and  the  total 
growth  reduced  to  less  than  one-half.  Toxic  effects  evident  in  the 
top  portions  of  this  culture  are  manifestly  to  be  associated  mainly 
with  the  greatly  increased  copper  content  of  its  roots,  since  total 
amounts  of  copper  in  the  top  portions  remain  small.  The  0.05 
per  cent  culture  of  copper  in  the  form  of  Cu=S,  or  finely  powdered 
chalcocite,  showed  only  faint  toxic  effects  in  the  tops.  The  fol- 
lowing summary  indicates  the  relation  between  toxic  effects  and 
copper  content  of  materials. 


416      University  of  California  Publications  in  Agricultural  Sciences    [Vol.  1 

Cu         Cu 
in  tops  in  roots 
Culture  Condition  p. p.m.     p. p.m.    Ratio 

Copper  carbonate,  0.01%  Cu     Leaves    faintly    striped 

(precipitated)  normal   weight  6.50    152.00    1:23 

Copper  carbonate,  0.025%  Cu     Leaves  strongly  striped 

(precipitated)  three-fourths    yellow, 

half  weight  21.00    728.00    1:34 

Copper  sulphide,  0.05%  Cu        Faintly    striped    leaves, 

normal  weight  12.50    171.00    1:13 

In  this  table  a  general  relation  is  shown  between  the  toxic 
effects  in  the  aerial  portions  of  the  plant,  and  the  amounts  of 
copper  in  root  systems :  but  as  to  the  soils  employed  toxic  effects 
are  influenced  both  by  amounts  and  character  of  copper  com- 
pounds present,  as  is  shown  further  on  following  pages. 

In  view  of  the  fact  that  the  small  increase  of  copper  in  the 
carbonate  cultures,  from  0.01  to  0.025  per  cent,  caused  severe 
toxic  effects  attended  by  an  increase  of  copper  in  root  systems 
from  152  to  728  p.p.m.  of  dry  matter,  it  seemed  desirable  to  in- 
vestigate thoroughly  the  quantitative  relations  between  the  copper 
in  roots  and  the  toxic  effects  as  shown  in  vegetative  growth.  It 
was  expected  in  this  way  to  find  a  means  of  determining  whether 
a  plant  contained  an  injurious  or  killing  dose  of  copper,  jusi  as. 
analogously,  killing  doses  of  poisons  in  animals  may  be  ascer- 
tained. With  this  end  in  view  cultures  of  corn,  beans,  and 
squashes  were  grown  in  water,  in  pots  of  soil  and  in  garden 
plots:  and  roots  and  top  portions  were  examined  quantitatively 
for  copper. 

In  preparing  samples  of  roots  for  analysis,  washing  with 
4  per  cent  hydrochloric  acid  was  carried  out  with  water  cultures, 
but  most  of  the  samples  were  prepared  by  washing  with  large 
quantities  of  copper-free  water  saturated  with  carbon  dioxide, 
until  the  washings  showed  no  trace  of  copper.  By  still  a  third 
method  the  soil  adhering  to  a  sample  was  analyzed  for  copper, 
the  ash  was  then  determined  and  assumed  to  be  soil,  and  a  cor- 
responding amount  of  copper  subtracted  from  the  total  found. 
For  details  see  "Methods  of  Analysis."  All  of  these  methods 
undoubtedly  give  conservative  figures  for  copper  in  root  systems 
inasmuch  as  solvents  not  only  remove  externally  adhering  com- 
pounds but  may  also  gradually  act  upon  the  copper  content  of 


1917]     Forbes:  Irrigation  Effects  of  Copper  Compounds  Upon  Crops       417 

root  systems.  The  acid-wash  and  soil-correction  methods  give 
severely  minimum  results.  The  carbon  dioxide  wash  used  in  the 
majority  of  analyses  is  laborious  but  more  satisfactory. 

Water  Cultures  (1907) 

Cultures  of  corn,  beans,  and  squash  were  grown  in  University 
of  Arizona  well-water  containing  250  p. p.m.  of  soluble  solids. 
Prom  0.03  to  3.0  parts  of  copper  as  precipitated  carbonate  dis- 
solved in  carbon  dioxide  were  used  in  making  cultures  and  the 
resulting  growths  of  tops  and  roots  were  divided  into  the  worst- 
poisoned  and  least-poisoned  portions,  for  determinations  of 
copper. 


Fig.  3. — Com  cultures,  series  121-62,  grown  in  University  of  Arizona 
well  water,  containing  from  .03  to  3.  parts  per  million  of  copper  as  basic 
carbonate    (Cu(OH),.CuC03). 


Series  Corn  121-62. — Grown  in  well  water  containing  Cu  as 
Cu(OH).,.CuCO,  as  follows:  check,  3.0,  1.0,  0.8,  0.5,  0.3,  0.1, 
0.08,  0.05",  and  0.03  p.p.m.  Cu.  December  1-February  27,  1907. 
Series  divided  into  two  portions: 

a.  Plants  not  badly  poisoned;  roots  growing;  tops  showing 
Cu  effects;  0.1,  0.08,  0.05,  0.03  cultures.     (Nos.  3694,  3693.) 

b.  Plants  badly  poisoned;  root  growth  arrested;  tops  living; 
3.0,  1.0,  0.8,  0.5,  and  0.3  cultures.     (Nos.  3692,  3691.) 

Scries  Beans  121-66. — Grown  in  well  water  containing  Cu 
as  Cu(OH),.CuC03  as  follows:  check,  3.0,  1.0,  0.8,  0.5,  0.3,  0.1, 
0.08,  0.05,  0.03  p.p.m.  Cu.  December  9-February  27,  1907. 
Series  divided  into  two  portions : 

a.  Least  poisoned  plants ;  roots  nearly  normal,  tops  normal ; 
0.3,  0.1,  0.08,  0.05,  0.03  cultures.     (Nos.  3702,  3697.) 


418      University  of  California  Publications  in  Agricultural  Sciences    [Vol.  1 

b.  Worst  poisoned  plants;  roots  badly  affected,  tops  less  af- 
fected; 3.0,  1.0,  0.8,  and  0.5  cultures.     (Nos.  3700,  3699.) 

Series  Squash  121-66.— Grown  in  well  water  containing  Cu 
as  Cu(OH)„.CuC08  as  follows:  check,  3.0,  1.0,  0.8,  0.5,  0.3,  0.1, 
0.08,  0.05,  and  0.03  p.p.m.  Cu.  December  10-February  27,  1907. 
Series  divided  into  two  portions : 

a.  Least  poisoned  plants ;  roots  growing ;  tops  strong ;  0.3,  0.1, 
0.08,  0.05,  and  0.03  cultures.     (Nos.  3698,  3701.) 

b.  Worst  poisoned  plants;  roots  dead  or  nearly  so:  tops  badly 
affected;  3.0,  1.0,  0.8,  and  0.5  cultures.     (Nos.  3696,  3695.) 

TABLE  XI 

Copper  Content  of  Plants  in  Water  Cultures 

Dry  Cu 

matter  Cu  p.p.m.  dry  matter 

Condition   of        in  found,  , *- x 

No.            Series                                                  sample         grams  grams  tops          roots 

3694  Corn,  .1,  .08,  .05,  .03         Tops  affected    0.3  .00009  14.30 

3693     Corn,   .1,  .08,   .05,  .03         Roots  growing   2.3  .000236  102.60 

3692     Corn,  3.,  1.,  .8,  .5,  .3  Tops  living       4.8  .000056     11.70 

3691     Corn,  3.,  1.,  .8,  .5,  .3         Roots  arrested   2.8  .000572  204.30 

3702     Beans,  .3,  .1,  .08,  .05,  .03  Tops  normal      9.4  .000198     21.10 

3701     Beans,  .3,  .1,  .08,  .05,  .03  Roots  growing   2.6  .000157  60.40 

3700     Beans,  3.,  1.,  .8,  .5  Tops  affected    6.6  .000204     30.90 

3699     Beans,  3.,  1.,  .8,  .5  Roots  badly 

affected  1.6  .000494  308.80 

3698     Squash,  .3,  .1,  .08,  .05,  .03  Tops  strong     10.4  .000333     32.00 
3697     Squash,  .3,  .1,  .08,  .05,  .03  Roots  nearly 

normal  .6  .000087  145.00 

3696     Squash,  3.,  1.,  .8,  .5  Tops  badly 

affected  3.6  .000092     26.00 

3695  Squash,  3.,  1.,  .8,  .5  Roots   dead  .2  .000058  290.00 


It  is  noteworthy,  in  this  series,  that  the  amounts  of  copper 
found  in  roots  that  still  retain  the  power  of  growth  average 
about  103  parts  in  one  million  of  dry  matter,  as  compared  with 
268  parts  in  dead  roots  whose  protoplasm  is  presumably  killed  as 
an  effect  of  copper.  Badly  poisoned  roots  in  every  instance  show 
a  great  excess  of  copper  over  those  less  affected.  The  tops,  on 
the  other  hand,  do  not  show  copper  in  proportion  to  the  amounts 
in  the  roots,  averaging  the  same  amount  of  copper  in  badly 
poisoned  (22.9  p.p.m.)  and  in  slightly  poisoned  (22.5  p.p.m.) 
plants.  Corn  was  observed  to  be  distinctly  more  sensitive  to 
copper  in  water  culture  than   either  squash   or  beans,   as   was 


1917]     Forbes:  Irrigation  Effects  of  Copper  Compounds  Upon  Crops       419 

shown  by  the  method  of  measuring  growth  of  root  tips  marked 
with  India  ink,  and  noting  points  at  which  growth  was  retarded 
(R)  and  arrested  (A). 

TABLE  XII 

Showing  Points  at  which  Eoots  were  Retarded  or  Arrested  in  Growth 

Cultures  iu  Cu,  in  well  water, 

parts    per    million    03        .05        .08        .1        .3        .5        .8        1.       3. 

Corn    R  A 

Beans    R  A 

Squash    R  A 

Photographs  of  the  three  series  also  indicate  an  earlier  re- 
tardation of  corn  root  development  than  of  bean  or  squash  root 
development ;  and  show  additionally  that  the  top  portions  of 
cultures  are  not  damaged  in  proportion  to  the  root  systems. 


TOXICITY  OF  COPPER  SOLUTIONS  TO  PLANT  ROOTS 
IN  WATER  CULTURE 

In  order  to  gain  some  indication  of  effects  in  water  culture 
of  copper  salts  upon  plants,  several  series  of  plants  were  grown 
under  varying  conditions,  and  effects  observed  of  the  kind  of 
copper  salts  employed,  strength  of  solution  used,  the  kind  of 
plant,  and  the  effects  of  other  salts  present. 

Solutions  were  made  in  water  free  from  copper,  twice  dis- 
tilled ;  or,  where  permissible,  University  of  Arizona  well  water, 
copper-free.  The  series  were  arranged,  usually,  to  carry  0.01, 
0.03,  0.05,  0.08,  0.1,  0.3,  0.5,  0.8,  1.0,  3.0,  and  5.0  parts  copper 
per  million  of  water.  The  cultures  were  made  in  600-c.c.  bottles, 
covered  with  pasteboard  squares  saturated  with  hot  paraffin  and 
perforated  with  three  holes  for  plant  seedlings  held  in  place  by 
cotton. 

Effects  upon  cultures  were  judged  by  elongation  of  roots  de- 
termined by  the  usual  method  of  marking  with  India  ink  5  mm. 
back  of  root  tips  and  noting  growth  after  twenty-four  hours. 
Corn,  beans,  and  squash  were  the  plants  employed  and  the  points 


420      University  of  California  Publication*  in  Agricultural  Sciences    [Vol.1 


particularly  noted  were  those  at  which  growth  was  retarded  and 
at  which  it  was  arrested. 

Table  XIII  gives  the  data  condensed  from  the  experimental 
records : 

TABLE  XIII  (a) 

Toxic  Effects  of  Copper  upon  Roots  of  Water  Cultures 

First   experiment    (1905) 

Cu  in  solution 


Culture 
Beans 

Copper   salt 
employed 

CuSO, 

Kind  of 
water 

Distilled 

Growth  retar 
between,  p.p 

ded 
m. 

Growth  arrested 
between,  p. p.m. 

.25—1.25 

Beans 

Cu(OH),.CuC03 

Well 

.57—5.7 

Cantaloi 

pes 

CuS04 

Distilled 

less  than  .25 

Cantaloi 

pes 

Cu(OH),.CuC03 

Well 

.57—5.7 

Indicating  lessened  toxicity  in  well  water. 


^wrr%?  it*  *f  m 


Pig.  4. — Bean  cultures  (eighth  exp.),  showing  effects  of  varying  con- 
centrations ei'  copper  in  distilled  water  and  in  solutions  of  mixed  salts. 
S,  salt  solutions;  1),  distilled  water;  W,  no  copper,  and  .05  to  3.  parts  per 
million  of  copper. 

TABLE  XIII   {b) 
Eighth  experiment  (1905) 


Corn 

Cu(OH),.CuC03 

Salt  solution* 

.3  —  .5 

.8 

— 1. 

Corn 

Cu(OH):.CuC03 

Distilled 

less  than  .01 

.1 

—  .3 

Beans 

Cu(OH),.CuCOs 

Salt  solution  ' 

.1  —  .5 

.8 

— 1. 

Beans 

Cu(OH)2.CuC03 

Distilled 

.1  —  .3 

.5 

—  .8 

Squash 

Cu(OH)2.CuC03 

Salt  solution 

.1  —  .5 

.8 

— 1. 

Squash 

Cu(OH)2.CuC03 

Distilled 

.1  —  .3 

.3 

—  .5 

Showing 

lessened  toxicity  in 

salt  solution. 

*NaCl 

64    jits. 

Na,S04 

2 

CaS04 

7.3 

Univ.   w 

ell 

water  salts  26.1 

Total         100    pts.  per  100,000. 


1917)     Forbes:  Irrigation  Effects  of  Copper  Compounds  Upon  Crops       421 

TABLE  XIII  (c) 

Fifth  experiment   (1905) 

Com  CuS04  Distilled  .01—  .05  .1  —  .5 

Con)  Cu(OH)2.CuC03       Distilled  .01—  .05         .1  —  .5 

Indicating-  equal  toxicity  of  Cu  as  sulphate  and  as  carbonate,  and  (com- 
pare second,  fourth  and  eighth  experiments)  great  toxicity  to  corn  in 
distilled  water. 

TABLE  XIII   (d) 
Third  experiment   (1905). 

Beans  CuS04  Distilled  .1  —  .3 

Beans  Cu(OH)2.CuCOa       Distilled  .1  —  .3 

Toxicity   to  beans  of  Cu   as   sulphate   and  as   carbonate  was   the   same 

TABLE  XIII  (e) 
Seventh    experiment    (1905) 

Squash  CuS04  Distilled  .01—  .05         .1  —  .5 

Squash  Cu(OH)2.CuC03       Distilled  .01—  .05         .1  -      .5 

Toxicity  to  squash  of  Cu  as  sulphate  and  as  carbonate  was  the  same. 

TABLE  XIII  {f) 

Second  experiment   (1905) 

Cu  in  solution 


Culture 

Copper  salt 
employed 

Kind  of 
water 

Corn 

Cu(OH)2.CuC03 

Well 

Bi'IlllS 

Cu(OH)2.CuC03 

Well 

Growth  retarded  Growth  arrested 

between,  p. p.m.  between,  p. p.m. 

.1  --  .3  .8  —1. 

.1  —  .3  .8  —1. 


Toxicity  of  copper  as  Cu(OH)2.CuC03  to  corn  and  beans  was  the  same. 

TABLE  XII 1   (a) 
Fourth  experiment  (1905) 

Corn  Cu(OH)2.CuC03       Well  .05—  .08         .8  —1. 

Squash  Cu(OH),.CuC03       Well  .1  —  .3  .8  —1. 

Corn  was  somewhat  more  sensitive  to  copper  as  Cu(OH)2.CuC03  than 
squash. 

TABLE  XIII  (7() 
Sixth  experiment   (1905) 

Beans                    Cu(OH)2.CuC03       Well  .1  —  .3         1.     —3. 

Squash                  Cu(OH)=.CuC03       Well  .1  --  .3           .8  —1. 

Beans  and  squash  were  about  equally  sensitive  to  copper  as  Cu(OH)2.- 
CuC03 

These  experiments,  which  are  not  stated  in  complete  detail 
here,  indicate  quite  clearly : 

1.  That  the  toxic  effects  of  copper  are  less  in  the  presence  of 
the  salts  ordinarily  contained  in  well  waters  than  in  distilled- 


422     University  of  California  Publications  in  Agricultural  Sciences  [Vol.  1 

water  solution.  This  fact  indicates  that  the  toxicity  of  copper 
salts  in  the  presence  of  soil-water  solutions  is  probably  minimized. 
In  all  cases  it  was  observed  that  root  growth  was  much  more 
vigorous  in  salty  than  in  distilled  water,  where  no  copper  was 
used.  Lessened  toxicity  of  copper  in  salty  solutions  may  there- 
fore in  part  be  due  to  greater  vigor  and  resistant  qualities  of 
plant  cells  grown  in  such  solutions. 

2.  Copper  appears  to  be  equally  toxic  as  sulphate  or  as  basic 
carbonate. 

3.  Corn  is  probably  more  sensitive  to  copper  salts  than  is 
squash  or  beans. 

Stimulation  Effects  in  Water  Cultures 

In  view  of  the  debated  question  as  to  stimulation  of  plant 

growth  by  minute  amounts  of  copper  salts,  it  is  of  interest  to 

observe  that,  quite  consistently,  the  most  vigorous  root  growth 

is  associated  with  concentrations  of  from  0.01  to  0.1  parts  per 

million  of  copper,  as  shown  by  details  from  cultures  described 

on  previous  pages. 

TABLE  XIV  (a) 

Stimulation  Effects  of  Copper  upon  Roots  of  Plants  in  Water 

Cultures 

Corn  roots  grown  in  well  water  with  Cu(OH)2.CuC03 

Condition 

Tops  of  plants  showing 
increased  growth  at  .08 
and  .1  p. p.m. 


Cu  p.p.m. 

Elongation  48  hrs. 

check 

23.4  mm. 

.01 

27.3 

.03 

17.6 

.05 

17.3 

.08 

19.4 

.1 

18.5 

Showing  stimulation  at  .01  p.p.m. 

TABLE  XIV  (fc) 
Bean  roots  grown  in  well  water  with  Cu(OH)2.CuC03 


Cu  p.p.m. 

Eli 

ligation 

48  hrs. 

Condition 

check 

2.5  mm. 

Tops    of    plants    in    .08 

.01 

2.2 

and    .1    cultures    higher 

.03 

4.7 

than  in  .05,  .03,  .01,  and 

.05 

2.8 

check. 

.08 

2.5 

.1 

2.9 

Showing  stimulation  at  .03  p.p.m. 


1917]     Forbes:  Irrigation  Effects  of  Copper  Compounds  Upon  Crops       423 

TABLE  XIV  (c) 
Corn  roots  grown  in  well  water  with   Cu  (OH)2.CuCOs 


Cu  p.p.m. 

Elongation  48  hrs. 

Condit 

check 

14.2  mm. 

vigorous 

.03 

17.3 

most    vigorous 

.05 

14.4 

most    vigorous 

.08 

9.6 

retarded 

.1 

10.3 

retarded 

Showing  stimulat: 

ion 

at  .03  p.p.m. 

Cu  p.p.m. 

Elongation  48  hrs. 

check 

2.4  mm. 

.03 

3.1 

.05 

4.5 

.08 

2.8 

.1 

3. 

TABLE  XIV  (d) 
Squash  roots  grown  in  well  water  with  Cu(OH)2.CuC03 

Cu  p.p.m.  Elongation  48  hrs.  Cu  p.p.m  Elongation  48  hrs. 

check  12.0  mm.  .08  12.3 

.03  10.7  .1  13.2 

.05  10.0 

Showing  no  stimulation  at  these  concentrations. 

TABLE  XIV  (e) 

Bean   roots  grown   in   well   water  with   Cu(OH)2.CuCOc 

Condition 
Tops     strong     through- 
out,    showing     stimula- 
tion  at   .03,   .05,   and   .1 


Showing  stimulation  at  .05  p.p.m. 

TABLE  XIV  (/) 
Squash  roots  grown  in  well  water  with  Cu(OH)2.CuC03 

Cu  p.p.m.  Elongation  48  hrs.  Cu  p.p.m.  Elongation  48  hrs. 

cheek  13.1  mm.  .08  7.6  mm. 

.03  7.4  .1  9.7 

.05  8.8  .3  3.7 

Not  showing  stimulation  consistently. 

TABLE  XIV  (g) 
Corn  roots  grown  in  well  water  with  Cu(OH)2.CuC03 

Elongation  48  hrs. 
13.5  mm. 
10. 

.05  17.5  .5  3.8 

Showing  strong  stimulation  .01  to  .1  mm. 


Cu  p.p.m. 
check 

Elongation  48  hrs. 
9.8  mm. 

Cu   p.p.m 
.1 

.01 

13.8 

.3 

4:22     University  of  California  Publications  in  Agricultural  Sciences  [Vol.  1 

water  solution.  This  fact  indicates  that  the  toxicity  of  copper 
salts  in  the  presence  of  soil-water  solutions  is  probably  minimized. 
In  all  cases  it  was  observed  that  root  growth  was  much  more 
vigorous  in  salty  than  in  distilled  water,  where  no  copper  was 
used.  Lessened  toxicity  of  copper  in  salty  solutions  may  there- 
fore in  part  be  due  to  greater  vigor  and  resistant  qualities  of 
plant  cells  grown  in  such  solutions. 

2.  Copper  appears  to  be  equally  toxic  as  sulphate  or  as  basic 
carbonate. 

3.  Corn  is  probably  more  sensitive  to  copper  salts  than  is 
squash  or  beans. 

Stimulation  Effects  in  Water  Cultures 

In  view  of  the  debated  question  as  to  stimulation  of  plant 

growth  by  minute  amounts  of  copper  salts,  it  is  of  interest  to 

observe  that,  quite  consistently,  the  most  vigorous  root  growth 

is  associated  with  concentrations  of  from  0.01  to  0.1  parts  per 

million  of  copper,  as  shown  by  details  from  cultures  described 

on  previous  pages. 

TABLE  XIV  (a) 

Stimulation  Effects  of  Copper  upon  Roots  of  Plants  in  Water 

Cultures 

Corn  roots  grown  in  well  water  with  Cu(OH)2.CuC03 


Cu  p.p.m. 

Elongation 

48  hrs. 

Condition 

check 

23.4  mm. 

Tops   of   plants   showing 

.01 

27.3 

increased   growth   at   .08 

.03 

17.6 

and  .1  p.p.m. 

.05 

17.3 

.08 

19.4 

.1 

18.5 

Showing  stimulation  at  .01  p.p.m. 

TABLE  XIV  (ft) 
Bean  roots  grown  in  well  water  with  Cu(OH)2.CuC03 

Cu  p.p.m.  Elongation  48  hrs.                                  Condition 

check  2.5  mm.                 Tops    of    plants    in    .08 

.01  2.2                         and    .1    cultures    higher 

.03  4.7                         than  in  .05,  .03,  .01,  and 

.05  2.8                         check. 

.08  2.5 

.1  2.9 
Showing  stimulation  at  .03  p.p.m. 


1917]     Forbes:  Irrigation  Effects  of  Copper  Compounds  Upon  Crops       423 

TABLE  XIV  (c) 
Corn  roots  grown  in  well  water  with  Cu(OH)2.CuC03 


Cu  p. p.m. 

Elongation  48  hrs. 

Condil 

check 

14.2  mm. 

vigorous 

.03 

17.3 

most    vigorous 

.05 

14.4 

most    vigorous 

.08 

9.6 

retarded 

.1 

10.3 

retarded 

Showing  stimulation  at  .03  p. p.m. 

Cu  p. p.m. 

Elongation  48  hrs. 

check 

2.4  mm. 

.03 

3.1 

.05 

4.5 

.08 

2.8 

.1 

3. 

TABLE  XIV  (d) 
Squash  roots  grown  in  well  water  with  Cu(OH)2.CuC03 

Cu  p.p.m.  Elongation  48  hrs.  Cu  p.p.m  Elongation  48  hrs. 

check  12.0  mm.  .08  12.3 

.03  10.7  .1  13.2 

.05  10.0 

Showing  no  stimulation  at  these  concentrations. 

TABLE  XIV  (e) 
Bean   roots  grown   in   well   water  with    Cu(OH)2.CuC05 

Condition 
Tops     strong     through- 
out,    showing     stimula- 
tion  at   .03,   .05,   and   .1 


Showing  stimulation  at  .05  p.p.m. 

TABLE  XIV  (/) 
Squash  roots  grown  in  well  water  with  Cu(OH)2.CuC03 

Cu  p.p.m.  Elongation  48  hrs.  Cu  p.p.m.  Elongation  48  hrs. 

cheek  13.1  mm.  .08  7.6  mm. 

.03  7.4  .1  9.7 

.05  8.8  .3  3.7 

Not  showing  stimulation  consistently. 

TABLE  XIV  (g) 
Corn  roots  grown  in  well  water  with  Cu(OH)2.CuC03 

Elongation  48  hrs. 
13.5  mm. 
10. 

.05  17.5  .5  3.8 

Showing  strong  stimulation  .01  to  .1  mm. 


Cu  p.p.m. 

Elongation  48  hrs. 

Cu   p.p.m 

check 

9.8  mm. 

.1 

.01 

13.8 

.3 

Cu    p. p.m. 

Elongation  48  hrs. 

Cvi   p. p. in. 

check 

'_'.     mm. 

.1 

.05 

6. 

.5 

424      University  of  California  Publications  in  Agricultural  Sciences    [Vol.  1 

TABLE  XIV  (h) 
Com  roots  grown  in  distilled  water  with  Cu(OH)a.CuC03 

Cu  p. p.m.  Elongation  48  hrs.  Cu  p. p.m.  Elongation  48  hrs. 

check  '27.6  mm.                         .05                           5.7  mm. 

.01  1.8                                  .1                              2.7 

No  stimulation  ;  eccentric  results. 

TABLE  XIV  (*) 
Bean    roots   grown   in   well   water   with    Cu(OH)2.CuCO~ 

Elongation  48  hrs. 

6.    mm. 

.8 
Showing  stimulation  at  .05  to  .1  p. p.m. 

TABLE  XIV  (j) 
Bean   roots  grown   in   distilled  water  with   Cu(OH)2.CuCO.~, 

Cu  p. p.m.  Elongation   is  hrs.  Cu   p. p.m.  Elongation  48  hrs. 

check  .'!.    mm.  .1  3.1  mm. 

.01  3.  .3  1.6 

.05  3.7 

Showing  no  stimulation. 

TABLE  XIV   (/.) 
Squash  roots  grown  in  well  water  with   Cu(OH)2.CuC03 

Cu   p.p.m.  Elongation  48  firs  Cu   p. p.m.  Elongation   is  Ins 

cheek  2.4  mm.  .1  5.7  mm. 

.05  4.9  .5  .4 

Showing  stimulation   at  .05  to  .1   p.p.m. 

TABLE  XIV   (0 
Squash   roots  grown    in   distilled   water   with   Cu(OH)2.CuC03 

Cu  p.p.m.  Elongation  48  hrs.  Cu   p.p.m.  Elongation  48  hrs. 

check  '■'•.'■'>  nun.  .05  3.1  mm. 

.01  3.3  .1  2.1 

Showing  no  stimulation. 

TABLE  XIV  (m) 
Bean    roots  grown   in    distilled   water  with   CuSO< 

Cu    p.p.m.  Elongation  48  his.  1  [eight  of  tops 

.1  2.9  mm.  87  mm. 

.3  1.2  91 

.5  .6  85 

Bean  roots  grown  in  distilled  water  with  Cu(OH)2.CuC03 
Cu   p.p.m.  Elongation  48  his.  Height  of  tops 

.1  2.9  mm.  98  mm. 

.3  1.  88 

.5  .6  84 

Showing  same  behavior  with  CuS04  and  Cu(OH)2.CuC03. 


1917 J     Forbes:  Irrigation  Effects  of  Copper  Compounds  Upon  Crops      42." 

TABLE  XIV   (n) 

SquasJi  roots  grown  in  distilled  water  with  CuS04 


Cu  p. p.m. 
check 
.01 


Elongation  24  hrs. 
3.6  mm. 

2.8 


Cu    p. p. in. 

.05 
.1 


Elongation  '24  hrs. 

1.4  mm. 

2 


Squash  roots  grown  in  distilled  water  with  Cu(OH)=.CuCOs 


Cu  p. p.m. 

check 
.01 


Elongation  24  hrs. 

3.6  mm. 

3.8 


Cu  p. p.m. 
.05 
.1 


Elongation  24  hrs. 
1 .1  mm. 
.4 


Doubtful  stimulation  at  .01  p. p.m. 


TABLE  XIV  (o) 
Corn   roots  grown  in  distilled  water  with  CuS04 


Cu  p. p.m. 

Elongation  48  hrs. 

check 

8.7  mm. 

.01 

10.9 

Corn   roots 

grown   in   distillec 

Cu    p. p.m. 

Elongation  48  hrs. 

check 

8.7  mm. 

.01 

13.2 

Cu   p. p.m. 
.05 
.1 


< 'n  p.p.m. 
.05 
.1 


Elongation  48  hrs. 
4.7  mm. 
1.5 


Elongation  48  hrs. 
3.3  mm. 
2. 


These  cultures,  while  somewhat  fragmentary,  afford  excellenl 
indications  of  stimulating  effects  upon  plant  roots.  Excluding 
squash,  which  is  not  satisfactory  material  to  work  with,  corn  and 
beans  show  consistent  stimulations  at  very  high  dilutions.  Meas- 
urements in  all  cases  are  averages  of  about  ten  observations. 


Experi- 
ment 

a 
b 
C 

e 

g 

h 

i 
j 
o 


TABLE  XV 
Summary  op  Stimulation  Effects 


Culture 
Corn  roots 
Bean  roots 
Corn  roots 
Bean  roots 
Corn  roots 
Corn  roots 
Bean  roots 
Bean  roots 
Corn  roots 
Corn   roots 


Copper  salt 
used 

CutOHh.CuCO, 

Cu(OH),.CuCO, 

Cu(OH),.CuCO:i 

Cu(OH),.CuCO:< 

Cu(OH),.CuC03 

Cu(OH),.CuC03 

Cu(OH),.CuCO:t 

CuCOH^.CuCO, 

CuSO, 

Ctt(OH),.CuCOs 


Character  and  strength  in  copper  of 
solution  producing  stimulation 


Well  water" 
at  .0]    p.p.m. 
.03 
.03 
.05 
.01-.1 


Distilled  water 


.05-.! 


none  at  .01  or  above 

none  at  .01  or  above 
.01 
.01 


426      University  of  California  Publications  in  Agricultural  Sciences    [Vol.  1 

Only  at  very  high  dilutions  (one  part  of  copper  to  from 
10,000,000  to  100,000,000  of  water)  are  accelerations  of  root 
growth  observed.  These  occur  with  both  corn  and  beans,  in  well 
water.  In  distilled  water  stimulation  was  observed  only  at  the 
highest  dilution — 1 :100,000,000.  In  well  water  stimulation  was 
observed  at  from  1:100,000,000  to  1 :10,000,000— consistently 
with  the  well  known  fact  that  in  presence  of  other  soluble  salts 
the  effects  of  copper  are  lessened. 


EFFECTS  OF  SOIL  UPON  TOXICITY  OF  COPPER 
SOLUTIONS 

Of  prime  importance  in  connection  with  possible  toxic  effects 
of  copper  in  soils  are  the  various  reactions  (1)  converting  in- 
soluble into  soluble  compounds,  (2)  reconverting  these  again  into 
insoluble  combinations,  and  (3)  modifying  the  toxic  effects  of 
copper  salts  in  solution. 

As  shown  in  the  table  of  solubilities,  both  basic  carbonate  of 
copper  and  chrysocolla  are  soluble  in  carbon  dioxide,  forming 
solutions  which  in  water  cultures  are  highly  toxic  in  character. 
Sulphides  of  copper  are  first  oxidized  to  the  sulphate,  which  is 
easily  soluble  : 

Cu2S  +  50  =  CuS04  +  CuO 
For  instance.  100  grams  of  chalcocite  ore  containing  3.2  per  cen1 
copper  were  shaken  in  a  flask  with  600  e.c.  of  water,  frequently, 
during  twenty-eight  days.     At  the  end  of  that  time  500  c.c.  of 
solution  contained  0.0132  grams  of  copper. 

Copper  sulphate  then  reacts  in  the  soil  to  form  various 
insoluble  compounds  with  consequent  lessening  of  toxic  action. 
With  calcium  carbonate  the  following  represents  a  reaction  which 
may  occur : 

2  CuS04  +  2  CaC03  +  H20  =  Cu(OH)2.CuC03  + 

2  CaS04  +  C02 

For  instance,  two  grams  of  precipitated  carbonate  of  lime  were 

added  to  an  excess  of  ten  grams  of  copper  sulphate  in  one  liter 


6  "University  of  Arizona  well  water"  contains  250  p.p.m.  of  soluble 
solids,  mainly  sodium  sulphate. 


1917]     Forbes:  Irrigation  Effects  of  Copper  Compounds  Upon  Crops       427 

of  water,  and  digested  with  frequent  shaking  for  over  four 
months,  the  green  precipitate  being  then  filtered  off,  dried  and 
analyzed  for  copper : 

Weight  of  precipitate  taken 100.00  mg. 

Cu  found  47.85 

Theoretical  Cu  in  basic  carbonate 57.38 

Indicating  by  the  formula  above  a  conversion  to  basic  carbonate 
of  copper  of  over  83  per  cent  of  the  solid  carbonate  of  lime  pres- 
ent. Bicarbonate  of  lime  in  solution  also  reacts  with  copper 
sulphate  to  form  the  basic  carbonate 

CaH2(C03)2  -f  4  CuSCvS  H,0  =  2  Cu(OH)2.CuC03  + 

CaS04  +  3  H2S04  +  16  H20 
3  CaH2(C03)2  +  3  H2S04  =  3  CaS04  +  6  H,0  +  6  C02 

The  silicates  of  the  soil,  also,  and  particularly  those  of  zeolitic 
character,  react  readily  with  soluble  copper  compounds  to  form 
insoluble  copper  silicates.  Organic  matter  likewise  combines 
with  large  amounts  of  copper,  to  form  compounds  of  indefinite 
or  unknown  composition.  As  a  result  of  all  these  reactions,  when 
soils  are  shaken  up  with  solutions  of  copper  salts  the  latter  are 
withdrawn  from  solution  in  large  amount.  Under  irrigation  con- 
ditions, where  waters  containing  minute  amounts  of  copper  are 
filtered  through  relatively  large  masses  of  soil,  this  action  is 
nearly  or  quite  complete. 

Five  large  percolators  were  arranged  with  varying  depths  of 


TABLE  XVI 
Percolation  op  Copper  Solutions  Through  Soils 

Solution  used 


Soil 

Depth 

Sandy   loam 

1  in. 

Sandy   loam 

5  in. 

Sandy  loam 

9  in. 

Sandy  loam 

1  in. 

Heavy  clay 

containing 

.003%   Cu 

12  in. 

Heavy  clay 

containing 

.003%   Cu 

12  in. 

Cu  compound  p.p.m 

Cu  ( OH )  2.CuC03  in  CO,  water  95 

Cu  ( OH )  2.CuC03  in  C02  water  95 

Cu  ( OH )  2.CuC03  in  C02  water  95 

Cu  ( OH )  2.CuC03  in  C02  water  56 


Cu  ( OH )  2.CuC03  in  C02  water  8.5 


Cu  in     Amount  of  Copper  in 
solution,    percolate,    percolate, 
p.p.m. 

none 


c.c. 
2000 
1500 
2000 
2000 


600 


none 

none 

.85 


CuSO,.5  ILO 


254 


150 


7.3 


428      University  of  California  Publications  in  Agricultural  Sciences    [Vol.  1 

soil  resting  on  filter  paper  supported  by  a  perforated  porcelain 
plate.  Two  soils,  heavy  clay  and  sandy  loam,  were  employed ; 
and  two  copper  solutions,  sulphate  and  bicarbonate. 

In  nearly  all  cases  copper  as  basic  carbonate  was  entirely 
removed  from  solution  in  percolating  through  as  little  as  a 
single  inch  of  sandy  loam.  Although  appreciable  amounts  of 
copper  sulphate  passed  out  of  a  soil,  the  latter  in  that  case  itself 
contained  a  very  small  percentage  of  copper.  Inasmuch  as 
soluble  copper  in  irrigating  waters  must  be  present  ordinarily 
as  basic  carbonate,  its  complete  withdrawal  by  thin  layers  of  soil 
is  significant  in  connection  with  irrigated  crops. 


Irrigation  Experiments 
A  set  of  cultures  was  arranged  to  test  the  effects  upon  crop 
plants  of  solutions  of  basic  copper  carbonate  so  applied  as  to 
filter  through  the  soil  before  reaching  the  plant  roots.     Six-inch 


Fig.  5. — Diagram  of  pot  culture  irrigated  through  two-inch  pot  inside. 

flower-pots  were  filled  with  sandy  loam  soil.  In  the  middle  of 
each  of  these  pots  a  two-inch  pot  was  half  buried,  and  the  plants 
experimented  with  were  grown  in  the  circles  of  soil  between  the 
large  and  small  pots.  These  plants  were  irrigated  by  pouring 
the  solution  used  into  the  small  pot,  through  the  bottom  of  which 
it  passed,  necessarily  filtering  through  more  or  less  soil  before 


1917]     Forbes:  Irrigation  Effects  of  Copper  Compounds  Upon  Crops      429 

reaching  the  plant  roots.  Radishes,  beans,  cantaloupes,  cucum- 
bers, lettuce,  peas,  beets,  corn,  berseem,  avas,  onions,  barley,  and 
wheat  were  employed ;  corn,  barley,  and  wheat  being  especially 
successful  under  these  conditions.  All  cultures  were  in  pairs, 
one  of  each  pair  being  irrigated  with  solutions  of  basic  carbonate 
of  copper  in  C02-water,  and  the  check  cultures  with  water  only. 
In  all  other  particulars — original  strength  of  plants,  exposure 
to  light  and  air,  and  amount  and  time  of  watering — the  con- 
ditions were  identical. 

These  cultures  were  carried  on  in  a  greenhouse  set  aside  for 
the  purpose.  The  experiment  was  begun  in  November  and  ended 
the  following  March.  The  solutions  of  basic  carbonate  of  copper 
employed  contained  from  0  to  55  p. p.m.  of  copper,  averaging 
about  20  parts,  which  is  from  7  to  670  times  as  much  as  has 
been  observed  in  the  waters  of  the  Gila  River  from  time  to  time. 


TABLE  XVn 

Condition  at  Maturity  of  Cultures  Irrigated  with  Copper  Solutions, 
as  Compared  with  those  Irrigated  with  Water 


C,  copper  culture;  W,  check. 

Tops 
C  and   W.      The 


Badishes 


Beans        C  greener 


Lettuce 


Peas 

Beets 

Corn  Stimulated  ?     C 

showing   stronger 

Berseem  C    stimulated, 
earlier  bloom 


same   in    appear- 
ance and  weight 

C  and  W. 
About   the    same 

C  and  W. 
About   the   same 

C  and  W.     Aver- 
aging the  same 


Weighing  the 
same,  but   C  ap- 
pearing stronger 

C  more  advanced 
in  growth,  but 
not  so  heavy 


Roots 

The     same,     but     in     C 

roots    were    removed    J 

in.   from  inner  pot  hole 

Equal;  same  number  of 
nodules;  very  local  ef- 
fect of  Cu  at  pot  hole 

The  same  except  that  in 
C  roots  were  dead  fxj 
in.  under  pot  hole 

Both  C  and  W  having 
abundant  nodules. 

No  apparent  damage  by 
Cu 

Fewer  in  soil  under  pot 
hole  in  C,  otherwise 
equal 

Equally  developed,  both 
showing  strong  nodule 
development. 


430      University  of  California  Publications  in  Agricultural  Sciences    [Vol.  1 


Avas 


Onions 


Barley 


Wheat 


C   stimulated,   ma- 
tured over  twice 
as  much  grain 

< '  stimulated 
matured  20% 
more  grain 


Tops 
C  and  W. 
Same  apparent 
growth 


C  and  W. 
Same  general 
appearance 

The  same  in 
weight,  but  C 
matured  more 
grain 

Identical  appear- 
ance, but  C  ma- 
tured more  grain 


Roots 
In  C  roots  within  $  in. 
of  pot  hole  damaged. 
Both  C  and  W  show 
strong  nodule  develop- 
ment 

Very  little  local  effect 
of  Cu  just  under  inner 
pot  hole  in  C 

No  roots  in  C  for  space 
of  1  x  J  in.  under  inner 
pot  hole 

In  C  no  roots  under  in- 
ner pot  hole  for  space 
of   1$  x  i   in. 


In  practically  all  cases  a  distinct  but  very  local  effect  of 
copper  solutions  upon  plant  roots  under  the  inner  pot  hole  was 
observed.  For  a  distance  of  a  half-inch  or  less  from  the  small 
pot  hole  exposed  roots  were  dead  or  missing.  The  soil  in  this 
area  was  observed  in  two  instances  to  contain  0.25  and  0.45  per 
cent  copper,  respectively.  In  one  instance  80  per  cent  of  the 
copper  added  was  found  in  the  4:?  grams  of  soil  just  under  the 
bottom  of  the  little  pot,  showing  the  rapidity  with  which  copper 
is  removed  from  its  solutions  by  filtration  through  the  soil. 

The  tops  of  the  cultures  under  consideration  in  no  instance 
showed  injury,  but  in  certain  cases  were  in  a  distinctly  advanced 
condition.  The  amounts  of  copper  contained  in  material  derived 
from  these  cultures  are  as  follows : 


TABLE  XVII  (a) 
Copper  Content  of  Plants  Irrigated  with   Copper   Solutions 


P.p.m.  of 

Cu  in 

rv  matter, 

Cu 

dry 

grams 

grama 

material 

Sample 
No. 

3673     Wheat  and  barley  tops  grown  in  check 

3675         soil    containing    a    trace    (.0025    per 

cent)  of  copper  32.90       .000100         3.04 

3672  Tops  of  beans,  peas,  corn,  lettuce,  car- 
rots, cucumbers  and  avas  grown  in 
check   soil  133.00       .000350         2.60 


1917]     Forbes:  Irrigation  Effects  of  Copper  Compounds  Upon  Crops       431 


P. p.m.  of 
Cu  in 
Sample  Dry  matter,         Cu  dry 

No.  grams  grams        material 

3674     Tops    of    wheat    and    barley    irrigated 

3676         with  water  averaging  20  p.p.m.  cop- 
per          30.70       .000400       13.00 

Tops  of  beans,  berseem,  peas,  onions, 
lettuce,  beets,  radishes,  corn,  avas, 
barley,  and  wheat  irrigated  with 
water  averaging  20  p.p. in.  copper  ....      27.20       .000751 

3690     Roots  of  same    (washed  in  4  per  cent 

HC1)     8.30       .000750 


27.60 
90.00 


In  brief,  even  when  relatively  large  amounts  of  water  contain- 
ing excessive  quantities  of  soluble  copper  were  applied  and  the 
experiments  so  arranged  that  all  of  the  copper  remained  in  the 
limited  volumes  of  soil  employed,  no  general  injury  to  the  plants 
was  observed,  although  apparently  slight  stimulation  occurred  in 
some  cases.  Prolonged  irrigation  with  such  solutions  would  be 
required  to  saturate  the  soil  to  a  depth  sufficient  to  seriously 
injure  plants  grown  in  it. 


\       / 


Fig.  6. — Wheat  and  barley  irrigated  (C)  with  copper  solutions  filtered 
through  soil,  and  (W)  with  well  water.  Both  show  stimulated  growth  with 
copper. 


432      University  of  California  Publicatio7is  in  Agricultural  Sciences    [Vol.  1 

CULTURAL  EXPERIMENTS 

Pot  Cultures  with  Treated  Soils 

Pot  cultures  of  corn,  beans,  and  squash  were  also  grown  in 
soils  containing  copper  in  the  form  of  precipitated  carbonate 
(Cu(OH),.CuC03),  finely  powdered  (100-mesh)  chalcocite  or 
sulphide  ore,  and  finely  powdered  chrysocolla  or  silicate  ore. 
Large  glazed  stone  jars  containing  thirty-eight  pounds  of  soil 
were  used.  Effects  on  growth  were  observed  and  the  copper 
content  of  tops  and  of  root  systems  was  determined.  The  follow- 
ing tabulations  relate  to  the  work  done  in  this  direction,  the  state- 
ment showing  the  copper  content  of  corn,  bean,  and  squash  plants 
expressed  in  parts  per  million  of  copper  in  dry  matter. 


TABLE  XVIII 

Copper  Carbonate  Series  (1908),  Beans 

Sample 
No. 

Culture 

Cu 

in  soil, 
per  cent 

Appearance 

and  height 

of  plants 

Dry 
matter, 

grams 

Cu 
found,       r 
grams 

Cu   p. p.m.   in 

tops 

> 

roots 

Normal 

3944 

Beans 

Check 

39  in. 

16.6 

.00022 

13 

4013 

Beans 

Check 

.72 

.00033 

453 

3945 

Beans 

.01 

38 

17.2 

.00027 

16 

4014 

Beans 

.01 

1.35 

.00116 

859 

3946 

Beans 

.025 

39 

15.9 

.00033 

21 

4015 

Beans 

.025 

1.21 

.00115 

950 

Toxic 

effects  begin  at  about  .035% 

Cu  in  soil 

Stunted 

3947 

Beans 

.05 

30 

13.2 

.00031 

23 

4016 

Beans 

.05 

1.09 

.00148 

1358 

3948 

Beans 

.1 

25 

6.7 

.00011 

16 

4017 

Beans 

.1 

1.44 

.00212 

1472 

3949 

Beans 

.25 

14 

3.7 

.00009 

25 

4018 

Beans 

.25 

1.35 

.00243 

1800 

3950 

Beans 

.5 

15 

2.9 

.0001 

35 

4019 

Beans 

.87 

.00147 

1690 

3951 

Beans 

1. 

12 

2.2 

.00009 

41 

4020 

Beans 

1. 

.53 

.00106 

2000 

3952 

Beans 

1.5 

14 

2.1 

.00009 

44 

4021 

Beans 

1.5 

.5 

.00115 

2300 

Containing  traces  of  copper,  .0025%. 


1917]     Forbes:  Irrigation  Effects  of  Copper  Compounds  Upon  Crops       433 


Fig.    7. — Bean   cultures    grown    in    soils   containing   copper    as    precipitated 
carbonate,  from  none  to  1.5  per  cent  Cu. 


TABLE 

XIX 

(  lOPPEB 

Carbonate  Series    (1907),  Corn 

Sample 

No. 

3870 

Culture 
Coin 

Cu 
in  soil, 
per  cent 

Check5 

Dry 

matter, 
grams 

45.2 

Cu 

found, 
grams 

.00(120 

Cu  p.p. 

m.    in 

tops 
4.40 

> 
roots 

3885 

Corn 

Check4 

8.8 

.00035 

40.00 

3860 

Corn 

.01 

1  75.0 

.00115 

6.50 

3868    . 

Corn 

.01 

10.6 

.00161 

152.00 

3865 

<  lorn 

.025 

77.0 

.00160 

21.00 

3866 

Corn 

.025 

9.2 

.00670 

728.00 

3864 

Corn 

.05 

47.7 

.00103 

22.00 

3867 

Corn 

.05 

4.4 

.00328 

745.00 

3863 

Corn 

.10 

26.8 

.00079 

30.00 

3862 

( lorn 

.15 

9.8 

.00046 

47.00 

3861 

Corn 

.20 

14.4 

.00073 

51.00 

3860 

Corn 

.30 

4.6 

.00110 

239.00 

T  Containing  traces  of  copper,  .0025%. 


Fig.  8. — Corn  cultures  grown  in  soils  containing  copper  as  precipitated  car 
bonate,  from  none  to  .2  per  cent  Cu. 


434      University  of  California  Publications  in  Agricultural  Sciences    [Vol.  1 
Copper  Carbonate  Series  (1908),  Corn 


Sample 
No. 


3992 
3993 
3994 
3995 


Culture 


Cu 

iu  soil, 
per  cent 


Corn  Cheek* 

Corn  .0] 

Corn  .015 

Corn  .02 


Appear- 
ance and     Dry 

height     matter, 
of  plants   grams 
Normal 
43  in. 
41 
35 
41 


7.48 
2.35 
4.07 
5.31 


Cu 

found, 
grams 

.00058 
.00049 
.00171 
.00397 


Toxic  effects  begin  at  about  .023%  Cu  in  soil 

Stunted 
33  in. 

15 


3996 
3997 
3998 

4000 


Corn 
Com 
Corn 

Corn 


.025 

.05 

.10 

.20 


22 
20 


4.81 
.31 
3.62 
1.99 


.00245 
.00023 
.00651 
.00444 


Cu  p.p.m. 

roots 


78.00 
209.00 
420.00 

748.00 


509.00 

742.00 

1798.00 

2231.00 


Containing  traces  of  copper,  .0025%. 


Copper  Carbonate  Series  (1908),  Squash 


Sample 
No. 


3937 
3938 
3939 
4026 
Toxic 

3940 
394] 


Appear- 

Cu        ance  and        Dry  <  u 

in  soil,        height       matter.  found, 

Culture          percent    of  plants     grains  grams 

Normal 

Squash         check       16  in.    11.2  .00016 

Squash         .01             16            6.3  .(10023 

S,|ii;isli           .025           15              9.2  .00031 

Squash         Chk.,  .01,  and  .025    .24  .00004 

■fleets  begin  at  about  .035%  Cu  in  soil. 

Blanched    and 
stunted 

.05  11  in.       3.7  .00017 

.10  11  2.3  .00014 


Squash 
Squash 


Cu   p.p.m. 


tops 

1  4.00 
36.00 
39.00 


Ml. (Ml 

61.00 


169.00 


Fig.  9. — Corn  cultures  grown  in  soils  containing  copper  as  sulphide   (chalco- 
eite),  from  none  to  1.  per  cent  Cu. 


1917]     Forbes:  Irrigation  Effects  of  Copper  Compounds  Upon  Crops       435 


TABLE  XX 

Chalcociti 

:  Series 

(1908) 

Sample 
No. 

Culture 

Cu 

in  soil, 
per  cent 

Appear 
ance  and 

height 
of  plants 

Dry 

matter, 
grams 

Cu 
found, 
grams 

Cu 

p. p.m.    in 

A 

tops 

roots 

Normal 

3979 

Corn 

Check 

*    36  in. 

17.60 

.00026 

15.00 

3979c 

Corn 

Check 

4.62 

.00027 

58.00 

3980 

Corn 

.01 

33 

11.60 

.00011 

10.00 

3980c 

Corn 

.01 

2.94 

.00023 

78.00 

3981 

Corn 

.02 

38 

19.40 

.00021 

11.00 

3981c 

Corn 

.02 

6.14 

.00114 

186.00 

3982 

Corn 

.03 

35 

17.90 

.00028 

16.00 

3982c 

Corn 

.03 

6.99 

.00176 

252.00 

3968 

Corn 

.05 

45 

51.70 

.00065 

13.00 

3978 

Corn 

.05 

6.14 

.00105 

171.00 

Toxic 

effects 

begin  at  about  .08%  Cu  in 

soil. 

Stunted 

3983 

Corn 

.10 

36  in. 

14.0(1 

.00031 

22.00 

3983c 

Corn 

.10 

yellow 

6.08 

.00625 

1028.00 

3984 

Corn 

.50 

8  in. 

3.20 

.00040 

125.00 

3984c 

Corn 

.50 

.47 

.00065 

1383.00 

3985 

Corn 

1.00 

12 

3.20 

.00050 

159.00 

3985c 

Corn 

1.00 

.49 

.00089 

1816.00 

Containing  traces  of  copper,  .00257^. 


The  cultures  described  in  the  foregoing  tables  indicate  sev- 
eral interesting  facts  more  or  less  applicable  to  field  conditions. 

(1)  Precipitated  carbonate  of  copper  is  shown  to  have  a 
much  more  toxic  effect  upon  corn  than  the  finely  pulverized 
ores  of  ehalcocite  or  chrysocolla.  With  the  precipitated  car- 
bonate 0.025  per  cent  in  the  soil  was  distinctly  toxic,  while  with 
ehalcocite  and  chrysocolla  about  0.08  per  cent  was  required  to 
produce  an  ecpial  effect.  Inasmuch  as  all  of  these  combinations 
of  copper  may  occur  in  a  soil  subject  to  mining  detritus,  a  mere 
determination  of  total  copper  in  soils  containing  doubtfully  toxic 
quantities  cannot  convey  trustworthy  information  as  to  the  in- 
juriousness  of  the  amounts  present. 

Moreover,  since  it  has  been  shown  that  in  the  case  of  pre- 
cipitated carbonate,  and  sulphate  of  copper,  eqiiivalent  quantities 
of  these  salts  in  solution  are  equally  toxic,  it  is  probable  that  the 
greater  toxicity  of  the  carbonate  is  due  to  its  greater  solubility 
under  soil  conditions.    It  is,  in  fact,  shown  in  table  I,  "Solubili- 


43(5      University  of  California  Publications  in  Agricultural  Sciences    [Vol.  1 


TABLE  XXI 

Chrysocolla  Series 

(1908) 

Sample 

Culture 

Appear- 
Cu        anee  and 
in  soil,       height 
per  cent   of  plants 

Dry 

matter, 
grams 

Cu 

found, 
grams 

Cu 

p. p.m.    in 

A 

No. 

tops 

roots 

Normal 

4003 

Corn 

Check*    32  in. 

25.60 

.00025 

10.00 

4003c 

Corn 

Cheek 

6.46 

.00012 

19.00 

4004 

Corn 

.05           33 

23.50 

.00026 

11.00 

4004c 

Corn 

.05 

6.70 

.00062 

93.00 

Toxic 

effects 

begin  at  about  .08%  Cu  in  soil. 

Dwarfed 

11  Ml.", 

Corn 

.10           30  in. 

17.90 

.00024 

13.00 

4005c 

Corn 

.10        striped 

5.82 

.00094 

162.00 

400(3 

Corn 

.10           28  in. 

10.50 

.00017 

16.00 

4006c 

Corn 

1.00         yellow 

4.29 

.00233 

543.00 

Containing  traces  of  copper,  .0025%. 


Pig.  K).     ('din  cultures  grown  in  soils  containing  copper  as  silicate  (chryso- 
colla), from  none  to  1.  per  cent  Cu. 


tics  of  Copper  Compounds,"  that  precipitated  copper  carbonate 
is  soluble  to  the  extent  of  1.5  parts  in  1,000, 000  of  water,  while 
copper  sulphide  is  soluble  to  the  extent  of  0.09  parts  of  copper 
in  1,000,000  of  water.  It  is  most  probable,  also,  that  the  finely 
divided  condition  of  the  precipitated  carbonate  is  more  favorable 
to  solution,  and  also  to  reaction  with  the  acids  of  plant  roots. 

(2)  Corn  is  seen  to  be  distinctly  more  sensitive  to  the  car- 
bonate of  copper  than  either  beans  or  squash.  With  corn,  toxic 
effects  appear  with  0.02  per  cent  of  copper  in  the  soil,  while 
with  beans  and  squash  these  toxic  effects  do  not  appear  until 
0.0:5;")  per  cent  of  copper  in  the  soil  is  reached.     As  is  suggested 


1917]     Forbes:  Irrigation  Effects  of  Copper  Compounds  Upon  Crops       437 

in  the  following  pages,  the  physical  constitution  of  root  systems 
may  account  in  part  for  varying  degrees  of  sensitiveness  to  cop- 
per compounds. 

The  presence  of  copper  in  tops  and  roots  of  check  is  due  to 
0.0025  per  cent  of  copper  in  the  soil  which  was  supposed  orig- 
inally to  be  free  from  this  element. 

Pot  Cultures  with  Field  Soils 
Two   field    soils   containing   copper    from    irrigating   waters 
were  tested  in  pot  culture  with  reference  to  toxic  effects  and 


Fig.  11. — Pot  cultures  of  coin  in  field  soils  containing  tailings.  No.  3887, 
.027%  Cu;  no.  3888,  .047%  Cu ;  and  no  copper.  Cultures  in  field  soils  are 
slightly  affected. 

copper  content  of  root  systems.  The  soils  employed  were  from 
a  field  showing  varying  effects  of  accumulations  of  tailings,  im- 
mediately southeast  of  Safford : 

Cu 
in  soil, 
Sample  per  cent 

3887  Sandy  loam,  surface  12  in.  of  soil  recently  put  under  irri- 

gation     027 

3888  Heavy   clay    (tailings)    mixed   with   sandy   loam,   surface    12 

in.,  long  under  irrigation,  much  tailings  047 


In  these  two  soils,  differing  mainly  through  the  addition  of 
tailings  to  No.  3888,  cultures  of  corn,  beans,  and  squash  were 
made,  and  examined  for  copper  with  the  following  results : 


438      University  of  California  Publications  in  Agricultural  Sciences    [Vol.  1 


TABLE  XXII 
Cultures  in  Tailings  Soils 


No.  Pot  culture  Condition 

3887  Corn   in   sandy    loam        Distinctly    striped 

3888  Corn    in    sandy  loam     Less  distinctly 

and  tailings  striped 

3887  Beans   in   sandy  loam     Normal   appearance 

3888  Beans   in   sandy  loam     Normal   appearance 

and    tailings 

3887  Squash  in  sandy  loam      Yellow    and    stunted 

3888  Squash  in  sandy  loam      Normal    appearance 

and    tailings 


Cu 
in  soil, 
per  cent 

.027 


Cu  p. p.m.  in 


tops 


.047 
.027 
.047 

.027 
.047 


28.00 
19.00 

73.00 
45.00 


roots 
453.00 

163.00 

1523.00 

703.00 


Pig.  12. — Showing  effects  of  copper  uie»<li ii«-<l  by  tilth  of  soil.    Strong  growth, 
lumpy  mixture;   weak  growth,  thoroughly  mixed. 


Bean  cultures  appeared   little  affected   by  copper  in  either 

No.  3887  or  No.  3888;  but  squash  was  distinctly  damaged  in 
No.  3887,  being-  yellow  and  stunted.  The  leaves  of  both  cultures 
of  corn  were  paler  Hum  (hose  of  the  check,  but  in  soil  No.  3887, 
containing  less  copper,  the  Leaves  of  corn  were  more  distinctly 
striped  than  in  No.  3SSS.  This  is  probably  due  to  the  sandy 
character  of  No.  3887  with  consequently  decreased  adsorptive 
action  upon  copper  salts.  Lumpiness  in  the  heavier  soil  might 
also  account  for  a  lessened  toxie  action,  as  indicated  by  an 
experiment  in  which  0.1  per  cent  of  copper  in  the  form  of  pre- 


1917]     Forbes:  Irrigation  Effects  of  Copper  Compounds  Upon  Crops       439 

cipitated  carbonate  was  mixed  (1)  intimately  and  (2)  in  lumpy 
condition.     Results  were  as  follows: 

Sample  Cu  as  pptd.  Cu  p. p.m. 

No.  carbonate,  per  cent  Condition  in  roots 

3998c         0.1   well    mixed  22  in.  high,  much  blanched  1798.00 

3999c         0.1  lumpy  28  in.   high,  mostly  green  457.00 

In  these  instances  it  may  be  noted  that  toxic  effects  are  asso- 
ciated with  higher  copper  content  of  roots  of  plants,  rather  than 
with  copper  content  of  soils  employed. 

As  in  other  cultures  it  is  observed  that  beans,  though  carry- 
ing a  higher  copper  content  than  corn,  show  less  toxic  effects — 
a  fact  possibly  to  be  explained  by  the  higher  protein  content  of 
the  plant  with  a  consequently  greater  capacity  for  absorption 
of  copper  before  toxic  effects  appear. 


Pot  and  Plot  Cultures 

In  order  to  carry  experimental  cultures  further  towards  field 
conditions,  cultures  of  wheat  and  corn  in  small  plots  of  sandy 
loam  garden  soil,  2Vo  X  1<S  fi'd,  were  grown,  copper  in  the  form 
of  finely  powdered  sulphate  having  been  thoroughly  spaded  in 
four  times  to  a  depth  of  nine  inches  in  the  amounts  shown  in 
table  XXIII.  The  roots  of  these  cultures  were  harvested  and 
examined  as  usual  for  copper. 

TABLE  XXIII 

Corn  Grown  in  Garden  Plots  Containing  Cu  Applied  as  CuS04  (1914) 


Dry 

Cu 

Cu 

Sample 

Cu  added. 

Condition 

matter, 

found, 

p.p.m. 

No. 

per  cent 

of   leaves 

grams 

grams 

roots 

5858a 

none 

Solid  green 

11.0 

.00015 

14.00* 

Toxic  effects 

begin  at  about  .008%  Cu  in 

soil. 

5859a 

.01 

Distinctly  yellow  striped 

11.6 

.00117 

101.00 

5860a 

.025 

Distinctly  yellow  striped 

8.6 

.00211 

246.00 

5861a 

.05 

Distinctly  yellow  striped 

7.3 

.00215 

296.00 

5862a 

.10 

Strongly  yellow   striped 

4.3 

.00300 

698.00 

5863a 

none 

6.2 

.00013 

21.00* 

Probably   resulting  from   roots   spreading  to   copper   soils. 


440      University  of  California  Publications  in  Agricultural  Sciences    [Vol.  1 

TABLE  XXIV 
Wheat  Grown  in  Garden  Plots  Containing  Cu  as  CuS04  (1914) 


Sample 
No. 

Cu  added, 
per  cent 

Condition 
of  leaves 

Dry 
matter, 
grams 

Cu 
found, 
grams 

Cu 
p.p.m. 

in  roots 

5648a 

none 

29   in.   high;    good 

4.46 

.00012 

27.00 

5649a 

.01 

29   in.   high;    good 

3.16 

.00190 

601.00 

Toxic  effects 

begin  at  about  .02%  Cu  in 

soil. 

5650a 

.025 

25-27   in.   high;    affected 

3.23 

.00260 

805.00 

5651a 

.05 

23  in.  high;  severely  af- 
fected 

1.90 

.00330 

1737.00 

5652a 

.10 

20  in.  high;  very  severely 
affected 

1.33 

.00200 

1504.00 

TABLE  XXV 

Wheat  Grown  in  Pots  to  Check  Plots  Containing  Cu  as  CuSO,  (1914) 


Sample 
No. 

Cu  added, 
per  cent 

Condition 
of  leaves 

Dry 

matter, 
grams 

Cu 

found, 
grams 

Cu 
p.p.m. 

in  roots 

5672a 

.0025 

Green;   27  in.  high 

1.51 

.00007 

46.00 

Toxic  effects 

begin  at  about  .005%  Cu  in  soil 

5673a 

.01 

Yellowish;    23   in.   high 

1.96 

.00035 

179.00 

5674a 

.025 

Yellow    and    stunted;    17 
in.  high 

.84 

.00030 

357.00 

5675a 

.or, 

Yellow    and    stunted;    12 
in.    high 

.52 

.00031 

593.00 

5676a 

.10 

Yellow  and  stunted;  4-12 
in.  high 

.30 

.00044 

1476.00 

The  corn  series  contains  much  smaller  proportions  of  copper 
in  the  roots  than  either  of  the  wheat  series,  a  fact  explained  in 
part  by  the  coarser  roots  of  corn,  which  therefore  have  less  ab- 
sorptive surface  in  proportion  to  their  weight.  Wheat  roots 
grown  in  plots  show  much  more  copper  than  pot  samples, 
although  the  copper  is  much  more  toxic  to  the  plants  in  pots 
than  in  plots,  a  contradiction  not  easily  understood  unless  it 
be  that  other  less  favorahle  conditions  of  growth  in  pots  were 
responsible  for  the  backward  condition  of  the  plants. 

Field  Samples  of  Soils  and  Vegetation 

In  order  to  relate,  if  possible,  the  experimental  work  detailed 
on  previous  pages  to  samples  of  field  material,  roots  of  barley, 
wheat,  oats  and  corn,  were  collected  in  the  district  studied  and 
the  amounts  of  copper  in  them  determined.    The  samples  of  bar- 


1917]     Forbes:  Irrigation  Effects  of  Copper  Compounds  Upon  Crops       441 


TABLE  XXVI 

Copper  in  Soils,  and  in  Boots  of  Plants  Grown  in  Field  Soils  Contain- 
ing Mining  Detritus,  near  Solomonville  and  Safford   (1914) 

Dry  Cu  Cu  p. p.m.  in 

mutter,       found,      , -* ., 

Jan.  3,   1909  grams         grains         tops  roots 

4008a  Barley  tops  selected  for  toxic 
effects  from  tailings  soil  (Wm. 
Gillespie),  Solomonville,  under 
Montezuma  Canal  13.90     .00061     43.80 

40086     Barley  roots,  ditto  2.70     .00160  592.50 

4009a  Oat  tops  selected  for  toxic  effects 
from  field  one  mile  west  of  Solo- 
monville, under  Montezuma  Canal     28.30     .00121     42.70 

40096     Oat   roots,   ditto    2.55     .00025  98.00 

Per  cent 
Drv  Cu  Cu  p. p.m.      Cu  in  soils 

matter,     found,      , -*- N     shaken 

March,    1914  grams      grams      yellow  green    from  roots 

5544a  Barley  roots,  yellow  plants ..  3.78  .00037       98               .017 

5545a  Barley  roots,  green  plants ....  2.33  .00290               124                .006 

5546a  Barley  roots,   yellow   plants ..  3.41       lost       

5547a  Barley  roots,  green   plants  ....  3.80  .00047               123 

5548a  Wheat  roots,  yellow  plants ....  1.40  .00044     314               .054 

5549a  Wheat  roots,  green  plants 1.25  .00048               382                .014 

5550a  Barley  roots,  less  green 

plants  2.17  .00077     354 

5551a  Barley  roots,  stronger  plants  3.34  .00110               329 

5552a  Oat  roots,  yellow  plants  1.67  .00066     394               .050 

5553a  Oat   roots,  green   plants   1.77  .00030               169                .039 

5554a  Barley  roots,  yellow  plants..  1.38  .00057     411                .073 

5555a  Barley  roots,  green  plants  ....  1.42  .00041                289                .032 

Average     314     236     .048     .023 

4010       Corn  roots   (1908)   in  tailings 

soil,  Solomonville  16.12     .00097  60 

November,    1914 

5841a     Corn  roots,  tailings  9  in.  deep  10.18  .00021  21 

5842a     Corn  roots,  tailings  8  in.  deep  11.08  .00038  34 

5843a     Corn  roots,  old  tailings  10.01  .00038  38                .055 

5844a     Corn   roots,   tailings    6-12   in. 

deep   21.48  .00039  18 

5845a     Corn  roots,  old  tailings  16.24  .00068  42 

5846a     Corn  roots,  old  tailings  5.02  .00034  68                .105 

5847a     Corn  roots,  old  tailings  14.42  .00104  72                .040 


Average     42 


442      University  of  California  Publications  in  Agricultural  Sciences    [Vol.  1 

ley,  wheat  and  oats  were  collected  in  sets  of  two  in  a  place.  One 
of  each  set  was  green,  healthy  growth,  the  other  more  or  less 
yellow  and  unthrifty  in  appearance.  The  object  of  this  method 
of  sampling  in  soils  found  to  contain  small  amounts  of  copper 
was,  if  possible,  to  relate  unthrifty  appearance  of  plants  exam- 
ined to  copper  found  in  roots  and  surrounding  soil.  Table  26 
(p.  441)  contains  the  results  of  the  determinations  made. 

As  may  be  expected  under  field  conditions,  which  are  more 
complex  and  variable  than  those  of  plot  or  pot  cultures,  these 
data  are  considerably  contradictory.  Roots  of  yellow  barley, 
wheat  and  oat  plants,  for  instance,  in  5544a  and  5548a  contain 
less  copper  than  roots  of  strong  green  plants  grown  alongside ; 
although  the  average  copper  content  (314  parts)  of  yellow  and 
more  or  less  unthrifty  plants  is  seen  to  be  greater  than  in  green 
plants  alongside  (236  parts).  So  far  as  observed,  the  larger 
percentages  of  copper  found  in  soils  shaken  from  roots  of  the 
plants  are  always  associated  with  yellow  plants.  The  average 
copper  content  of  soils  from  roots  of  yellow  plants  is  0.048  per 
cent,  while  that  from  green  plants  is  0.023  per  cent.  These 
observations  indicate  that  in  a  general  way  the  larger  amounts 
of  copper  found  in  these  field  soils  are  associated  with  larger 
amounts  of  copper  in  root  systems  and  with  yellow  color  in  young 
plants.  The  percentages  of  copper  observed  in  the  soil,  ranging 
up  "to  0.073  per  cent  in  one  instance,  is  surprisingly  high,  but 
toxic  effects  must  be  qualified  by  the  character  of  the  compounds, 
soluble  salts  in  the  soil,  and  other  factors  noted  on  preceding 
pages. 

Yellowness  of  foliage  also  may  be  due  to  other  causes  than 
copper.  Among  these  are:  (1)  too  much  water,  as  in  low  places; 
(2)  alkali  accumulations;  (3)  cold  weather;  (4)  too  much 
nitrogen  in  improper  form,  as  in  some  old  barnyards;  (5)  too 
little  available  nitrogen,  as  on  new  ground;  (6)  shade,  and  (7) 
insect  pests  and  plant  diseases.  Malnutrition  from  any  cause, 
in  fact,  usually  expresses  itself  in  the  yellow  or  striped  appear- 
ance of  the  leaves  of  these  crop  plants.  Such  appearance,  there- 
fore, cannot  be  attributed  to  copper  present  in  the  soil,  without 
exclusion  of  other  causes  and  sufficient  confirmatory  evidence. 

As  in  the  case  of  plot  and  pot  cultures,  corn  roots  are  ob- 


1917]     Forbes:  Irrigation  Effects  of  Copper  Compounds  Upon  Crops       443 

served  to  contain  much  less  copper  than  other  grain  roots  grown 
in  similar  soils,  a  fact  to  be  attributed  to  the  coarse  character 
of  field  samples  of  corn  roots. 

USE  OP  COPPER  SULPHATE  TO  KILL  MOSS  IN 
IRRIGATING  DITCHES 

Clear  irrigating  water  supplies,  such  as  are  derived  from 
seepage  and  from  wells,  quickly  become  choked  with  mosses  and 
algae  in  warm  weather,  entailing  loss  of  water  and  expensive 
ditch  cleaning.  In  order  to  test  the  application  of  copper  to 
a  running  stream  for  the  purpose  of  killing  the  growth  of 
aquatic  plants,  an  experiment  was  conducted,  in  October,  1906, 
upon  the  Flowing  Wells  ditch  near  Tucson,  which  at  the  time 
contained  abundant  aquatic  growth. 

A  barrel  of  copper  sulphate  solution  was  prepared  and  placed 
at  the  head  of  the  ditch.  By  means  of  a  small  outlet  controlled 
by  a  stopcock,  fifteen  pounds  per  hour  of  CuS04.5H,0  were 
added  to  the  ditch  flow,  this  amount  being  in  the  proportion  of 
1  part  of  copper  to  100,000  of  water.  Most  of  the  copper  was 
immediately  precipitated  by  the  bicarbonate  of  lime  present  in 
the  water ;  still  more  probably  combined  in  insoluble  form  with 
the  soil  along  the  ditch ;  while  the  remainder  acted  with  toxic 
effect  upon  the  sensitive  algae  and  the  less  sensitive  mosses 
(Potomogctons)  growing  in  the  water.  A  short  distance  below 
the  barrel,  where  algae  and  mosses,  after  twenty-five  hours'  ex- 
posure to  copper,  were  brown  and  dead  and  breaking  away  from 
their  points  of  attachment,  .84  parts  of  copper  in  1,000,000  of 
water  remained  in  solution.  Three  miles  below  the  barrel,  where 
the  mosses  and  algae  were  still  plainly  affected,  traces  only  of 
dissolved  copper  were  perceptible.  A  renewal  of  copper  from 
point  to  point  would  therefore  have  been  necessary  in  treating 
a  long  ditch  by  this  method,  which,  however,  proved  too  costly 
for  adoption  in  the  instance  mentioned.7 

It  is  of  interest  in  this  connection  to  note  that  in  the  early 
days  of  irrigation  on  the  Gila  River,  mosses  grew  in  such  abund- 
ance in  the  clearer  waters  obtained  from  the  river  at  that  time, 


"  See  Bibliography,  p.  488,  reference  31 


444      University  of  California  Publications  in  Agricultural  Sciences    [Vol.  1 

that  considerable  labor  was  required  to  keep  the  ditches  clean. 
These  mosses  have  now  entirely  disappeared  from  the  upper 
canals,  due  in  part  to  the  turbid  waters  in  which  they  will  not 
grow,  and  in  part,  perhaps,  to  the  dissolved  copper  from  the 
mines. 

PHYSIOLOGICAL  OBSERVATIONS  ON  TOXIC  EFFECTS 
OF  COPPER  SALTS 

Quantitative  Work 

Citrus  seedlings  placed  in  copper  sulphate  solutions  contain- 
ing from  2.5  to  100  parts  of  copper  in  1,000,000  of  distilled 
water  wilted  in  forty-eight  hours,  thus  showing  effects  of  toxicity. 
Root  tips  then  all  turned  red  with  K4FeCy„.  Red  root-tips 
sectioned  showed  under  low  power  red  cells  under  bark  and 
around  center.  Citrus,  cucumber  and  bitter  melilot  roots 
grown  in  10:1,000,000  copper  solution  all  gave  violet  reaction 
with  KOH,  less  delicate  but  more  distinctive  than  K4FeCyt!,  since 
the  purple  biuret  test  indicates  both  copper  and  protein. 

Cultures  of  wheat,  peas,  corn,  beans,  and  other  plants  thrown 
in  soils  containing  from  0.005  to  0.1  per  cent  of  copper  in  soil, 
gave  only  very  doubtful  root-tip  reactions  with  K4FeC\„, 
although  showing  evident  injury,  especially  in  0.1  per  cent  cul- 
ture. There  is  an  essential  difference  between  water-culture 
l-oots  placed  in  copper  solutions  and  roots  grown  in  soil.  The 
first  are  killed  by  excess  of  copper  salts  contained;  the  second 
are  yet  living  and  growing  resistantly  in  the  soil. 

A  0.1  per  cent  copper  culture  of  corn,  wheat,  beans  and 
cucumbers  was  washed  out  from  the  soil  and  gave  superficial  red 
coloration  with  K4FeCy(1,  but  not  internal.  Living  tissue  is 
evidently  inconsistent  with  sufficient  amounts  of  copper  to  give 
a  plain  internal  test.  Therefore,  the  small  amounts  of  copper 
known  to  be  in  poisoned  but  living  root  systems  must  be  dissem- 
inated. It  is,  therefore,  of  interest  to  know  the  copper-protein 
ratio  in  poisoned  but  living  root  systems,  such  a  ratio  being  more 
significant  than  the  ratio  of  copper  to  the  whole  mass  of  root 
systems,  which  includes  various  proximate  principles  not  con- 
cerned in  copper  fixation. 


1917 J     Forbes:  Irrigation  Effects  of  Copper  Compounds  Upon  Crops       445 

Two  assembled  samples  of  corn,  radish,  wheat,  vetch  and 
peas  grown  in  soils  containing  0.005  per  cent  and  0.05  per  cent 
of  copper  were,  therefore,  very  thoroughly  washed  out,  copper 
determined,  and  nitrogen  determined  X  6*4  for  protein.  The 
amount  of  copper  required  to  saturate  vegetable  protein  was 
assumed  at  11.7  per  cent  (14.655  per  cent  CuO) — the  average 
of  figures  given  in  Mann's  Chemistry  of  the  Proteids,  page  305. 

(1)  Roots  grown  in  .005%  Cu  in  soil  4739000  gm. 

Cu  .0105%    0000498 

N.  2.26%  =  Protein  14.125%  0669400 

Cu  required  for  saturation   of  protein 

.06694  gm.  X  11.7%  =  .007832  gm.  Cu  for  saturation 

.0000498 
Per  cent  saturated  = -----    =.637% 

(2)  Roots  grown  in  .05%  Cu  in  soil  3561000  gm. 

Cu    .0322%    0001147 

N.   2.76%=  Protein   17.25%    0614900 

Cu  required  for  saturation  of  protein 

.06149  gm.  X    11.7%  =  .007194  gm.  Cu  for  saturation 

L    ,       .0001147       ,  „„,_ 
Per  cent  saturated  =—--— — -  =  l.o94% 
.007 1 94 

Per  cent 
saturation 

Summary:  c"  P-P-™-  of  protein 

J  dry  roots  with  copper 

(1)  .005%  Cu  in  soil  105  0.636 

(2)  .05%  Cu  in  soil  322  1.594 

Ratio   (1)    to   (2)   3.07  2.51 

In  brief,  10  times  as  much  copper  in  the  soil  resulted  in  3 
times  as  much  copper  in  the  entire  root  systems  and  2.5  times 
as  much  in  the  protein  of  these  root  systems.  This  latter  in- 
crease, however,  is  responsible  for  an  increase  in  damage  from 
almost  nothing  to  very  severe. 

Further  observations  on  the  copper-protein  saturation  figure 
in  roots  grown  in  soil  containing  copper,  were  made  on  wheat 
and  Canada  peas,  planted  in  pots  containing  soil  mixed  with 
varying  percentages  of  copper  in  the  form  of  precipitated  basic 
carbonate.  The  pots  contained  102  pounds  of  sandy  loam,  and 
were  irrigated  in  a  uniform  manner  from  time  to  time  as  water 
was  needed.  Plantings  were  made  January  3,  1916,  and  roots 
harvested  May  15. 


446      University  of  California  Publications  in  Agricultural  Sciences    [Vol.  1 

TABLE  XXVII 

Observations   on   the   Saturation   with   Copper  of   Protein   in   Eoots 
Grown  in  Soil  Treated  with  Cu(OH)2.CuC03 


d 

6396 

'3 

X 

a 

^  a 
a  -- 

O    a; 
O  D. 

.005 

Material 
Wheat  roots 

x 

5 

^  u 

0  ^ 

2-S* 

'S  S 

^  x 

2.4726 

0  Weight  of  Cu  i: 
§  sample,  grams 

a 

X 

C 

c 

Pn   be 

.1069 

•    Cu  required  to 
2  saturate  protei 
to  grams, 
w  factor  11.7% 

_    0 

si* 

g  5'5 

P*    X    O. 

1.84 

6397 

.02 

Wheat  roots 

4.0122 

.00068 

.1660 

.0194 

3.50 

6398 

.06 

Wheat  roots 

2.2236 

.00068 

.1231 

.0144 

4.70 

6399 

.10 

Wheat  roots 

2.4658 

.00037 

.1401 

.0164 

2.25 

6401 

.005 

Canada  pea  roots 

2.6275 

.00085 

.3936 

.0461 

1.85 

6402 

.02 

Canada  pea  roots 

2.3844 

.00093 

.3684 

.0431 

2.16 

6403 

.06 

Canada  pea  roots 

2.0056 

.00053 

.2657 

.0311 

1.70 

6404 

.10 

Canada  pea  roots 

2.2708 

.00093 

.3747 

.0438 

2.12 

"While  the  figures  on  saturation  in  the  last  column  of  the 
table  vary  without  reference  to  the  amount  of  copper  in  the 
soil  and  the  degree  of  injury  observed  in  the  roots,  yet  they  all 
show  a  very  low  ratio  of  copper  found  to  copper  required  for 
saturation  of  protein  present. 

In  both  wheat  and  peas,  injury  was  first  shown  at  0.02  per 
cent  of  copper  in  soil,  increasing  greatly  with  higher  percentages. 
This  injury,  showing  as  a  characteristic  crinkly  condition,  is 
best  seen  in  wheat  and  corn  and  lias  been  observed  in  wheat 
roots  grown  in  a  soil  containing  as  little  as  0.017  per  cent  of 
copper. 

A  further  quantitative  study  of  copper  effects  on  root  sys- 
tems was  carried  out  in  water  culture  with  corn,  wheat,  and 
Canada  peas.  Paraffin  (parowax)  disks  one-third  of  an  inch 
thick  and  nine  inches  in  diameter  were  employed,  perforated 
with  holes  of  suitable  diameter  by  means  of  steel  cork  borers. 
These  disks  were  supported  on  paraffin  posts  two  and  one-half 
inches  high  in  four-quart  deep  graniteware  pans  containing  the 
water  culture  solutions  which  were  used.  After  soaking,  the 
germinating  seeds  were  planted  in  paraffin  disks  of  suitable 
perforation  and  nutrient  solution  was  then  poured  up  to  level 
of  contact  with  seeds.  At  first  tap-water  was  used;  then  a 
nutrient  solution  made  up  as  follows : 


1917]     Forbes:  Irrigation  Effects  of  Copper  Compounds  Upon  Crops       447 

KN03  1.0  gm. 

MgS04   05 

NaCl  5 

CaS04    5 

FeCl,    04 

Tap-water  1.0  liter 

No  phosphate  was  included  because  of  its  precipitating  action 
on  copper  salts.  After  the  cultures  were  about  four  weeks  old 
they  were  changed  to  nutrient  solutions  containing  small 
amounts  of  copper  which  was  gradually  increased  from  one  to 
ten  parts  per  million  of  solution.  The  solution  was  neutralized 
with  normal  H2S04  (methyl  orange  indicator)  to  prevent  pre- 
cipitation of  copper  by  dissolved  carbonates.  Following  is  a 
summary  of  the  history  of  the  cultures,  each  of  which  was  in- 
creased to  include  several  hundred  plants : 

Wheat 

Dec.  16  Planted  in  tap-water. 

Dee.  24  Transferred   to   nutrient   solution,   one-third   strength. 

Jan.     8  Changed  to  nutrient  solution,  two-thirds  strength. 

Jan.  14  To  nutrient  solution,  full  strength. 

Jan.  17  To  nutrient  solution  containing  1  part  Cu  per  million. 

Jan.  21  To  nutrient  solution  containing  2  parts  Cu  per  million. 

Jan.  25  To  nutrient  solution  containing  6  parts  Cu  per  million. 

Jan.  28  To  nutrient  solution  containing  10  parts  Cu  per  million. 

Feb.     9  Experiment  terminated. 

A  faint  biuret  test  appeared  after  addition  of  6  p. p.m.  Cu.  Also  dis- 
tinct K4FeCy0  test.  Boots  did  not  become  flaccid,  but  the  tops  of  cul- 
tures were  dying  back  and  prostrated  markedly  in  comparison  with  roots 
of  control  culture. 

Canada  Peas 

Dec.  20  Planted  in  tap-water. 

Dec.  30  Transferred  to  fresh  tap-water. 

Jan.     6  Transferred  to  fresh  tap-water. 

Jan.  18  Transferred    to    nutrient   solution. 

Jan.  20  Changed  to  nutrient  solution  containing  1  part  Cu  per  million. 

Jan.  21  To  nutrient  solution  containing  2  parts  Cu  per  million. 

Jan.  25  To  nutrient  solution  containing  6  parts  Cu  per  million. 

Jan.  28  To  nutrient  solution  containing  10  parts  Cu  per  million. 

Feb.  6-8  Experiment  terminated. 

A  faint  biuret  test  appeared  after  addition  of  6  p. p.m.  Cu.  Distinct 
K4FeCy„  test  in  root  tips  at  end  of  experiment.  Eoots  not  flaccid,  but 
plants  distinctly  affected  and  tops  dying  back  more  than  those  of  control 
culture. 


448      University  of  California  Publications  in  Agricultural  Sciences    [Vol.  1 

Corn 

Dec.  22  Planted  in  tap-water. 

Jan.     8  Changed  to  nutrient  solution,  one-third  strength. 

Jan.  19  To  nutrient  solution  containing  1  part  Cu  per  million. 

Jan.  21  To  nutrient  solution  containing  2  parts  Cu  per  million. 

Jan.  25  To  nutrient  solution  containing  6  parts  Cu  per  million. 

Jan.  28  To  nutrient  solution  containing  10  parts  Cu  per  million. 

Feb.     9  Experiment   terminated. 

Giving  distinct,  faint  biuret  test  after  addition  of  6  p.p.m.  Cu;  also 
K4FeCy„  test  at  end  of  experiment.  Roots  not  flaccid  at  end  of  experi- 
ment, but  tops  of  cultures  about  half  dead,  while  tops  of  control  culture 
were  still  in  good  condition. 

These  cultures,  as  shown  by  the  notes,  were  exposed  to  cop- 
per solutions — wheat  twenty-three  days,  peas  eighteen  days, 
corn  twenty-one  days.  At  the  end  of  the  experiment  roots  were 
not  flaccid,  but  very  faint  biuret  and  distinct  ferrocyanide  tests 
were  observed.  In  all  cases  top  growth  was  affected,  corn  most, 
wheat  next,  and  peas  least.  This  material,  as  indicated  above, 
is  poisoned  only  just  enough  to  show  reactions  in  root  tips, 
although  tops  are  distinctly  affected.  It,  therefore,  represents 
minimum  rather  than  maximum  toxic  conditions.  Material  was 
harvested  and  analyzed  to  show  copper  and  nitrogen  ratios ; 
and  by  estimating  the  number  of  root  tips  in  samples  of  corn, 
peas,  and  wheat  the  amount  of  copper  per  root  tip,  required  to 
show  faint  tests,  was  found. 


TABLE  XXVIII 

Quantitative  Determinations  on  Water  Cultures  Showing  Slight 

Toxic  Effects 

Corn 


No. 
6321 

Sample 
265   tops 

Pry  matter, 
grams 

17.695 

1  !u  found, 
grams 
.00048 

Cu  p.p.m.  in 
dry  matter 

27.10 

6320  | 
6323  j 

Coarse  roots 

2.4277 

.00022 

91.00 

6319 

1100   root   tips 

.77 

.00042 

545.50 

Amount  of  copper   per   root   tip   associated   with   slight   toxic   effects, 
.00042  -f-  1100  =  .000000382  gm. 


1917]     Forbes:  Irrigation  Effects  of  Copper  Compounds  Upon  Crops       449 


Peas 

Dry  matter,  Cu  found,  ('up. p.m.  in 

No.  Sample  grams  grams  dry  matter 

6327  250  tops  7.0850  .00012  16.90 

6325  Coarse  roots  1.2827  .00180  1400.00 

6326  Fine  roots  .8393  .00141  1680.00 
6324  5500  root  tips  .4462  .00153  3428.00 

Amount  of  copper  per  root  tip  required  to  show  slight  toxic   effects, 
.00153  H-  5500  =  .000000278  gm. 

Total  roots  examined  for  nitrogen   4.41730  gms. 

Albuminoids  in  roots  (Alb.  N.   X   6^)   83929 

Topper  required  to  saturate  albuminoids  (factor  11.7%)        .09819 
Total  Cu  found  00784 

Saturation  -°~  =  7.99% 

Wheat 

I >rv  matter.  Cu  found,  Cu  p. p.m.  in 

No.  Sample  grams  grams  drv  matter 

6332  530  tops  12.7  .00165  129.90 

6331  Roots  .6902  .00020  297.00 

6330  16000  root  tips         .3664  .00103  2811.00 

Amount   of  copper  per   root   tip   associated    with   slight   toxic    effects, 

.00103  -h  16000  =  .000000064  gm. 

Total  roots  examined  for  nitrogen  2. 9223  gms. 

Albuminoids  in  roots  (Alb.  N.   X  H)  30794 

Copper  required  to  saturate  albuminoids  (factor  11.7%)        .03603 

Total  Cu  found  001789 

Saturation  f™*  =  4.96% 


These  figures  show,  as  usual,  relatively  small  amounts  of 
copper  in  tops  of  plants,  with  large  amounts  in  roots,  increasing 
from  coarser  to  finer  portions,  until  in  the  root  tips  corn  con- 
tains 545,  peas  3428.  and  wheat  2811  parts  per  million  of  eopper 
in  dry  matter.  For  peas  and  wheat  these  are  the  largest  propor- 
tions of  copper  thus  far  observed  in  any  plant  samples. 

When  the  total  amount  of  copper  found  in  each  sample  is 
divided  by  the  number  of  root  tips  employed,  an  extraordinarily 
small  amount  of  copper  is  found  necessary  to  bring  about  toxic 
effects.     For  instance 

One  corn  root  tip  (terminal  3  cm.)  required 000000382  gms.  Cu 

One  pea  root  tip  (terminal  1  cm.)  required 000000278  gms.  Cu 

One  wheat  root  tip  (terminal  1  cm.)  required     .000000064  gms.  Cu 


450      University  of  California  Publications  in  Agricultural  Sciences    [Vol.  1 

Moreover,  the  extent  to  which  albuminoids  in  affected  roots 
are  saturated  with  copper — only  7.99  per  cent  for  peas  and  4.96 
per  cent  for  wheat — indicates  a  maximum  effectiveness  upon 
roots  of  small  amounts  of  the  metal. 

Reactions  of  Copper  with  Growing  Points 

Corn  seedlings  fifteen  days  old  were  fixed  with  cotton  in 
tall  50-c.c.  graduated  Nessler  tubes  containing  different  strengths 
of  copper  sulphate  in  pure  distilled  water.  The  strengths  of 
solution  employed  were  20,  10,  5,  2.5,  and  1.25  p. p.m.  There  was 
a  check  culture  with  no  copper.  After  three  days,  in  all  cases 
except  the  check,  the  roots  were  flaccid,  showing  contraction  on 
graduations  and  giving  biuret  and  ferrocyanide  tests,  increasing 
in  strength  from  weaker  to  stronger  concentration. 

An  experiment  with  pea  seedlings  gave  similar  results,  but 
when  the  quantity  of  pea  roots  was  increased  and  weak  solutions. 
2.5  and  1.25  p. p.m.,  were  employed  in  small  quantities  (20  c.c), 
the  tests  became  much  fainter. 

Severed  roots  of  corn,  also,  were  observed  to  give  as  good 
tests  as  roots  of  living  plants.  A  large  number  (seventy)  of 
severed  root  tips  placed  in  a  small  quantity  (20  c.c.)  of  weak 
solution  (5  p. p.m.)  gave  only  a  faint  ferrocyanide  test.  These 
observations  indicate  that  the  concentration  of  copper  in  growing 
points  is  due  to  ionic  dissociation  and  migration  through  the 
semi-permeable  membranes  of  the  root  systems, s  rather  than  to 
transpiration.  The  fainter  test  for  copper  in  large  quantities  of 
root  material  indicates  lessened  toxicity  of  dilute  solutions  of 
copper  in  presence  of  excess  of  root  materials. 

Mature  wheat,  corn  and  pea  plants  in  nutrient  solutions,  but 
not  growing  actively,  were  treated  with  gradually  increasing 
amounts  of  copper  from  January  21  to  February  2.  as  follows : 

Wheat,  Corn,  and  Pea  Plants,  Thirty-seven  Days  Old,  Treated  with 
Copper  in  Nutrient  Solution 

Jan.  12 1  —  2 ."> ;  nutrient  sol.  w.  2  p.p.m.  Cu. 
Jan.  25-28;  nutrient  sol.  w.  4  p.p.m.  Cu. 
Jan.  28  to  Feb.  5,  nutrient  sol.  w.  10  p.p.m.  Cu. 


s  See   Bibliography,    p.   488,   references   35,   36,   37,   38,   39,   40,   41,   42, 
43,  44. 


1917]     Forbes:  Irrigation  Effects  of  Copper  Compounds  Upon  Crops       451 

Feb.  5;   very  faint  biuret  test  for  copper,  distinct  ferrocyanide   test. 

Corn,  forty-eight  days  old  in  50  p.p.m.  Cu  sol.,  two  days,  gave  faint 
biuret  and  ferrocyanide  tests. 

Corn,  forty-eight  days  old  in  500  p.p.m.  Cu  sol.,  two  days,  gave  faint 
tests  for  copper. 

From  these  observations  it  is  evident  that  the  nearly  negative 
results  shown  are  due  either  to  nutrient  salts  present  or  to  the 
older  and  therefore  more  quiescent  material  employed.  To  settle 
this  question,  the  following  experiments  were  made: 

(1)  Young  (ten  days)  wheat  and  corn  plants  were  placed  in 
copper  solution  in  distilled  water  and  in  nutrient  solutions  and 
observed  after  twenty  and  forty  hours,  as  follows: 

2.5  p.p.m.  Cu,  distilled  water — 20  hours 
10  days  old:  Young  wheat;  flaccid?;  strong  biuret  test;  strong  K4FeCy6  test 
60  days  old:  Old  wheat;  not  flaccid;  no  strong  biuret  test;  distinct  K4FeCyc 

test 
10  days  old:   Young  corn;  flaccid;  strong  biuret  test;   strong  K4FeCy6  test 
(10  days  old :  Old  corn ;  flaccid ;  no  biuret  test ;  old  tips,  faint  K4FeCy6  test 

young  tips,  strong  K4FeCy„  test 

10  p.p.m.  Cu,  distilled  water — 20  hours 
10  days  old:  Young  wheat;  flaccid?;  strong  biuret  test;  strong  K4FeCy6  test 
(50  days  old:  Old  wheat;  not  flaccid;  faint  biuret  test;  distinct  K4FeCy6  test 
10  days  old:   Young  corn;   flaccid;   strong  biuret  test;   strong  K4FeCyb-  test 
60  days  old:   Old  corn;   flaccid?;   distinct  biuret  test;   strong  K4FeCy„  test 

40  p.p.m.  Cu,  distilled  water — 20  hours 
10  days  old:  Young  wheat;  flaccid;  strong  biuret  test;  strong  K4FeCy6  test 
60  days  old:   Old  wheat;   flaccid?;   faint  biuret  test;   distinct  K4FeCy6  test 
10  days  old:  Young  corn;  flaccid;  strong  biuret  test;  very  strong  K4FeCy„ 

test 
60  days  old:  Old  corn;  flaccid;  strong  biuret  test;  strong  K„FeCy,,  test 

The  above  results  indicate  that  old  roots  of  corn  and  wheat 
are  more  resistant  to  the  penetration  of  copper  than  are  the 
young  roots.  This  is  shown  by  less  flaccidity  in  the  weaker  solu- 
tions and  by  the  fainter  tests  observed.  A  second  series  with 
greater  strengths  (5,  20.  and  100  p.p.m.)  and  longer  exposure 
(forty-five  hours)  showed  distinctly  less  differentiation  than  in 
the  case  of  the  series  above  given  in  detail.  This  is  to  be  expected, 
inasmuch  as  stronger  solutions  must  overcome  resistance  of  roots 
exposed  to  them  more  quickly,  and  the  longer  time  employed 
would  likewise  tend  to  overcome  differences  existing  in  the  first 
few  hours  of  the  experiment. 


452      University  of  California  Publications  in  Agricultural  Sciences    [Vol.  1 

(2)  Young  and  old  wheat  and  corn  roots  were  placed  in  10 
p. p.m.  Cu  in  distilled  water  and  10  p. p.m.  Cu  in  nutrient  solution. 
with  the  following  results : 

10  p. p.m.  Cu,  distilled  water — 20  hours 
10  days  old:  Young  wheat;  flaccid?;  strong  biuret  test;  strong  K4FeCy„  test 
60  days  old:  Old  wheat;  not  flaccid;  faint  biuret  test;  distinct  K4FeCy0  test 
10  days  old:   Young  corn;  flaccid;  strong  biuret  test;  strong  K4FeCy„  test 
60  days  old:   Old  corn;   flaccid;   distinct  biuret  test;    strong  K4FeCyi;   test 

10  p.p.m.  Cu,  neutralized  nutrient  solution — 20  hours 
10  days  old:  Young  wheat;  not  flaccid;  doubtful  biuret  test;  faint  K4FeCyc 

test 
60  days  old:   Old  wheat;    not   flaccid;    none  or  doubtful  biuret  test;    faint 

K4FeCy6  test 
10  days  old:   Young  corn;   not  flaccid;    faint   biuret  test;    distinct   K4FeCy„ 

test 
60  days  old:   Old   corn;   not  flaccid;   distinct   biuret  test;   distinct  K4FeCy,, 

test 


This  shows  very  distinctly  the  prevention  of  toxic  action  upon 
plant  roots  through  the  protective  action  of  other  solids  in  solu- 
tion. ;is  already  observed  in  water  cultures  by  measurements  of 
root  growth.  It  is  noteworthy  in  this  connection  that  corn  roots 
generally  seem  to  be  more  sensitive  to  the  action  of  copper  salts 
than  the  roots  of  wheat  or  peas. 

In  order  to  examine  still  further  into  the  relative  resistance 
of  old  and  young  root  systems  to  copper  salts,  a  solution  of  5 
p.p.m.  Cu  in  distilled  water  was  used,  the  time  being  varied 
from  twenty  to  two  hundred  hours.  The  results  of  these  obser- 
vations indicate  that,  with  wheat  and  corn  roots,  the  penetration 
of  copper  is  distinctly  more  rapid  in  young  than  in  old  material. 
Peas  did  not  give  clear  results. 

It  appears  from  these  observations,  first,  that  the  accumula- 
tion of  copper  in  plant  roots  is  distinctly  due  to  the  migration 
of  dissociated  ions  into  the  root  systems,  where  they  are  fixed  by 
protoplasm,  in  which  combination  they  are  identified  by  means 
of  the  biuret  test.  Second,  the  presence  of  nutrient  salts  very 
distinctly  lessens  the  effect  of  a  Id  p.p.m.  copper  solution  upon 
sensitive  young  growing  plant  roots.  Third,  old  quiescent  plant 
roots  developed  in  a  nutrient  solution  are  distinctly  less  sensitive 
to  copper  salts  than  young  roots  which  are  still  actively  growing. 


1!»17]     Forbes:  Initiation  Effects  of  Copper  Compounds  Upon  Crops       453 

The  slow  development  of  biuret  tests  for  copper  in  such  material 
after  sufficient  exposure  to  copper  solutions,  indicates  the  presence 
of  protoplasm. 

It  is  possible  that  the  same  observations  may  apply  to  other 
poisons,  metallic  or  otherwise,  brought  into  contact  with  absorp- 


Fig.  13. — Photomicrograph  of  root  tip  of  corn  grown  in  water  culture 
and  poisoned  by  1:200,000  of  Cu  in  solution.  The  copper  is  shown  as  red 
copper  ferrocyanide,  which  appears  black  in  the  photomicrograph.  The 
irregular  inner  black  line  shows  the  penetration  of  the  copper  and  also 
indicates  sharply  the  differences  in  permeability  of  adjacent  cells,  some 
of  which  are  penetrated  before  others.  (X  80  diam.)  (Photo  by  J.  T. 
Barrett.) 


454      University  of  California  Publications  in  Agricultural  Sciences    [Vol.  1 

tive  root  systems  in  the  soil.  Not  only  this,  but  it  may  be  true 
that  nutrient  salts,  as  well,  will  be  found  more  actively  absorbed 
by  younger  and  more  sensitive  root  systems  than  by  older  ones, 
or  by  root  systems  which  for  any  reason  have  become  quiescent. 
This  would  suggest  the  possibility  of  choosing  to  advantage  the 
proper  time  for  applying  substances,  either  to  avoid  injury  or, 
as  in  the  case  of  fertilizers,  to  secure  maximum  benefit  from  them. 

Varying  Resistance  of  Individual  Cells  to  Copper 

Not  only  do  old  and  young  roots  vary  as  to  toxic  effects  upon 
them  of  copper,  but  different  degrees  of  resistance  between 
individual  cells  in  the  same  root  and  even  in  the  same  chain  of 
cells,  is  clearly  shown  in  the  photomicrograph  (fig.  13)  of  a 
corn  root  tip  which  has  been  exposed  to  a  1  to  200,000  solution 
of  copper,  then  colored  with  K4FeCy0,  and  sectioned  for  obser- 
vation. The  dark,  abruptly  angular  line  of  penetration  shown 
in  the  section  plainly  indicates  that  individual  cells  may  be 
penetrated  by  copper  while  adjacent  cells  growing  under  pre- 
cisely similar  physical  conditions  are  not  penetrated.  If  this 
be  not  due  in  some  unseen  way  to  morphological  peculiarities 
of  root  structure,  it  must  be  due  to  individuality  in  the  cells 
themselves,  some  of  which  must  be  more  resistant  to  penetration 
by  dilute  copper  solutions  than  others. 

Summing  up  the  physiological  observations  relating  to  effects 
of  copper  upon  plants,  we  find  (1)  that  individual  cells  vary 
(probably)  in  degree  of  resistance  to  penetration  by  copper 
salts;  (2)  that  young  roots  are  less  resistant  than  old  roots;  (3) 
that  roots  of  certain  species  of  plants  (e.g.  corn)  are  less  resist- 
ant than  roots  of  other  species;  and  (4)  that  toxic  effects  may 
be  to  some  extent  related  to  the  structure  and  distribution  of 
root  systems. 

DIAGNOSIS  OF  COPPER  INJURY 

In  the  presence  of  toxic  amounts  of  copper  in  the  soil,  the 
root  systems  of  culture  plants  become  harsh  and  crinkly  with 
almost  entire  loss  of  root  hairs.  Consistent  with  the  checking  of 
growing  points,  root  systems  are  also  greatly  restricted  in  extent, 


1917]     Forbes:  Irrigation  Effects  of  Copper  Compounds  Upon  Crops       455 

and  in  feeding  capacity.  Individual  roots  are  coarse,  covered 
with  thick  epidermis,  and  are  abruptly  angular,  apparently  as 
a  result  of  chemotropic  contortions.  Root  tips  are  shortened  and 
thickened  and  in  some  instances  are  strongly  proliferated.  The 
anatomical  structures  associated  with  these  changes  in  form  are 
very  striking.  In  corn  the  cells  of  the  primary  cortex,  in  normal 
roots,  are  elongated  parallel  with  the  axis  of  the  root,  and  in 
longitudinal  tangential  section  measured  about  74  by  30  microns. 
Injured  cells  of  corn  grown  in  soil  containing  0.1  per  cent  copper 
gave  longitudinal  tangential  sections  approximately  34  by  30 
microns,  as  shown  on  accompanying  drawings.  (See,  also,  plates 
6,  7,  and  8. 


HWn 


- 


<~ 


__ 


Fig.  14. — a.  Tangential  longitudinal  section  of  corn  root  grown  in  soil 
containing  .1  per  cent  of  copper  as  copper  sulphate,  showing  cells  of  cortex 
of  injured  rootlet,  b.  Tangential  longitudinal  section  of  normal  corn  root 
cells  of  cortex.     (X   ±  300  diam.)      (Sections  by  G.  F.  Freeman.) 

These  structural  modifications,  taken  in  connection  with  other 
symptoms  and  conditions  and  in  the  absence  of  other  causes, 
such  as  an  excess  of  alkali  salts,9  confirm  a  diagnosis  for  copper 
injury  in  a  soil  of  doubtful  toxicity.  For  instance,  March  4. 
1916,  two  sets  of  samples  of  barley  were  collected  in  the  district 
studied,  and  the  material  examined  for  evidence  of  copper  in- 
jury, a.s  follows : 

Lot  1. — Young  barley  plants  from  the  upper  end  of  a  field  midway 
between  Safford  and  Solomonville,  under  Montezuma  Canal.  The  soil  next 
the  ditch  shows  old  tailings,  and  there  are  irregular  areas  of  yellow 
barley  immediately  under  the  canal. 


3  See  Livingston,  Botanical   Gazette,  vol.  30,  no.  5,  p.  229,  1900. 


456      University  of  California  Publications  in  Agricultural  Sciences    [Vol.  1 

Sa^ple  a.  Yellow  bailey  plants 

6343  Boots,  crinkly  and  angular,  much  branched  near  surface. 

Dry  weight,  3.2429  gins ;  Cu,  .00085  gin ;   p.p.m 262 

6344  Soil  shaken  from  yellow  barley  roots 

Copper    07979% 

Total  soluble  solids  (alkali)  46400 

CI   as   NaCl   004 

Sodium    carbonate    008 

Nitrogen     137 

b.  Green  barley  plants   from  near   (a). 

6345  Roots,  smooth  and  straight,  not  much  branched  near  sur- 

face.    Dry  weight,  1.6025  gm;  Cu,  .0002  gm ;   p.p.m.—.      125 

6346  Soil  shaken  from  green  barley  roots 

Copper    05844% 

Total  soluble  solids  (alkali)   45600 

CI  as  NaCl   004 

Sodium   carbonate    none 

Nitrogen     181 

Lot  2.— Young  barley  plants  from  the  upper  end  of  a  field  in  West 
Layton  under  Montezuma  Canal.  Soil  near  ditch  known  to  contain  tail- 
ings and  showing  spots  of  yellow  bailey  at   head   of  field. 


Sample  o.   Yellow  barley  plants 

No.  ' 

6347  Roots,  crinkly  and  angular,  much   branched. 

Dry  weight,  3.2977  gins;   Cu,  .0014  gm ;   p.p.m 425 

6348  Soil  shaken  from  roots  of  yellow  barley  plants 

Copper    1 113% 

Total   soluble   solids    (alkali)    50 

CI  as  NaCl   008 

Sodium   carbonate    008 

Nitrogen     165 

b.  Green  barley   plants  from  near   (a) 

6349  Roots,  smooth,  straight,  not  much  branched. 

Dry  weight,  2.2473  gins;  Cu,  .0003  gm ;   p.p.m 133 

6350  Soil  shaken  from  roots  of  green  barley  plants 

Copper    02678% 

Total  soluble  soli. Is  (alkali)   40 

CI   as  NaCl   008 

Sodium    carbonate    004 

Nitrogen     127 


1917]     Forbes:  Irrigation  Effects  of  Copper  Compounds  Upon  Crops       457 

Considering  the  above  observations,  we  notice  that  the  soils 
from  which  samples  were  taken  do  not  contain  injurious  amounts 
of  soluble  salts.  Their  nitrogen  content,  also,  is  normal.  The 
areas  of  yellow  barley  from  which  samples  come  are  therefore  not 
to  be  attributed  to  alkali  salts,  or  to  abnormal  nitrogen  content. 
Observation  in  the  field,  also,  failed  to  indicate  that  conditions  of 
irrigation,  temperature,  or  light  were  unfavorable,  these  condi- 
tions being  the  same  for  both  green  and  yellow  samples. 

Excluding  these  considerations,  therefore,  we  now  find  that 
there  is  uniformly  more  copper  in  the  roots  of  yellow  barley 
plants  than  in  those  of  the  green  ones,  also  in  the  soils  in  which 
they  occur.  The  roots  of  yellow  plants,  moreover,  show  the 
crinkly  condition  caused  (though  not  exclusively)  by  copper 
when  present  in  toxic  amounts  in  the  soil.  The  following  state- 
ment summarizes  these  observations. 


Lot  1 


Cu   in   soil 

Cu   p. p. in 

per  cent 

in   roots 

Yellow  barley 

.0798 

262.00 

Green    barley 

.0584 

125.00 
Lot  2 

Yellow  barley 

.1113 

425.00 

Green    barlev 

.0268 

133.00 

Condition   of   roots 

Crinkly  and  branched 
Straight,  not  branched 


Crinkly  and  branched 
Straight,  not  branched 


The  evidence  therefore  indicates  quite  conclusively  that  the 
two  yellow  samples  owed  their  color  to  toxic  effects  of  copper 
upon  the  roots  of  the  young  plants.  Later  in  the  season,  how- 
ever, no  difference  in  mature  plants,  showing  variations  in  color 
when  young,  may  be  observed.  This  must  be  due  to  the  fact 
that  as  root  systems  penetrate  more  deeply  into  the  soil  they 
escape  the  surface  zone  of  tailings,  with  consequent  recovery 
from  the  effects  of  copper. 


458      University  of  California  Publications  in  Agricultural  Sciences    [Vol.  1 


Part  II.- GENERAL  DISCUSSION 

PRELIMINARY  STATEMENT 
The  copper  compounds,  in  solid  form  and  in  solution,  that 
result  from  mining  operations  in  the  Clifton-Morenci  district, 
have  found  their  way  down  the  San  Francisco  and  Gila  rivers 
to  the  underlying  irrigated  agricultural  soils  of  Graham  County 
in  sufficient  amounts  to  raise  the  question  of  their  toxicity  to 
crops.  The  largest  amounts  of  copper  in  these  soils  are  found 
at  the  heads  of  irrigated  lands,  especially  where  alfalfa  is  or 
has  been,  at  which  points  old  accumulations  of  tailings,  laid 
down  for  the  most  part  prior  to  1908,  are  still  to  be  found. 

Accumulations  of  Copper 

The  amounts  of  copper  accumulating  in  the  Gila  River  valley 
soils  in  this  way  are  small,  the  observed  range  being  from  0.006 
per  cent  to  0.111  per  cent  in  surface  soils  and  the  average  for 
eighteen  soils  analyzed  being  0.046  per  cent  of  copper.  Irrigated 
soils  elsewhere  have  been  observed  to  contain  larger  quantities 
of  copper  than  those  above  noted,  for  instance  1.002  per  cent  on 
the  Deer  Lodge  River  below  Anaconda.  Montana,  with  an  aver- 
age of  0.09  per  cent  for  eleven  other  samples  taken  in  the  same 
locality.10 

These  amounts  of  copper  in  a  soil  may  or  may  not  be  toxic 
according  to  the  combination  in  which  the  copper  exists,  the 
physical  character  of  the  soil  and  its  chemical  composition, 
climatic  and  moisture  conditions,  the  crop  grown,  and  other  con- 
siderations which  may  now  be  discussed  in  order. 

The  small  amounts  of  soluble  copper  constantly  coming  down 
stream  from  the  mines  which  cannot,  like  solid  tailings,  be  en- 
tirely excluded  from  irrigating  water  supplies,  are  of  importance 
because  of  their  tendency  to  accumulate  by  reason  of  the  fixing 
power  for  copper  of  silicates,  carbonates  and  organic  matter  in 
the  soil.  The  completeness  of  this  fixing  power  of  soil  for  copper 
is  shown  by  several  experiments  in  which  solutions  of  copper 


i»  IT.  S.  D.  A.  Bur.  Chem.,  Bull.  113,  p.  34,  1907. 


1917]     Forbes:  Irrigation  Effects  of  Copper  Compounds  Upon  Crops       459 

salts  were  percolated  through  one  to  twelve  inches  of  soils,  with 
little  or  no  copper  appearing  in  the  filtrates.  Under  field  con- 
ditions, therefore,  this  action  tends  to  concentrate  dissolved 
copper  in  irrigating  water  in  the  surface  few  inches  of  the  soil. 
A  series  of  samples  of  Montezuma  Canal  water  taken  at 
Solomonville  affords  quantitative  suggestions  in  this  connection : 

TABLE  XXIX 

Copper  Content  of  Gila  River  Waters 


pie  No. 
date 

May 

and 
26, 

I 
'04 

Description 

River  very  low 

Amounts  of  Cu  added 

in    irrigation,   estimated 

in  p. p.m.  of  water 

Approx. 

flow  of 

Gila 

River 

in  sec. 

ft. 

30 

Approx. 

amts.  of 

copper 

carried 

down 

stream, 

1  dav 

lb.' 

3094 

Sam 
3309 

In 

tailings    s 
18.3 

In 

olution 
.80 

Total 
19.1 

3486 

June 

11, 

'05 

Small  flood 

.25 

170 

230 

3622 

June 

25, 

'06 

River    low 

1.6 

.11 

1.71 

(Soluble 
only) 

3737 

Feb. 

22 

'07 

Medium   flood 

trace 

2.88 

±3.0 

600 

9720 

4011 

Jan. 

3, 

'08 

2.1 

.08 

2.18 

Tailings  shut  out 

of  river 

May 

1,  1908 

4029 

Apr. 

12, 

'09 

1.4 

.08 

1.48 

6342 

Mar. 

4, 

'16* 

.04 

.03 

.07 

*  Following  four-months  shutdown  of  operations  in  Clifton-Morenci 
district. 

These  figures,  while  somewhat  meagre,  seem  to  indicate  a 
lessening  waste  of  copper  downstream  following  the  restraint  of 
tailings  from  the  water-supply  in  May,  1908.  This  is  especially 
true  of  copper  in  solution,  due  probahly  to  the  decreased  amounts 
of  solid  copper  compounds  in  suspension  from  which  copper  in 
solution  is  derived. 

Assuming  at  the  present  time  an  average  of  1  part  of  copper 
in  1,000,000  of  Gila  River  water,  four  acre-feet  of  such  water, 
required  for  one  year's  irrigation,  would  contain  10.9  pounds 
of  copper,  from  which  should  be  deducted  small  losses  due  to 
vegetation,  drainage  waters,  and  percolation  to  depths  below  the 
surface  soil. 

Six  tons  of  alfalfa  with  a  copper  content  of  5  p. p.m.  contain 
0.06  lb.  copper;  while  one  acre-foot  of  seepage  water  (about  the 
annual  seepage  loss)  containing  0.25  p. p.m.  copper  would  carry 
0.68  lb.  copper.     Estimating  the  total  loss  roughly  at  one  pound 


4:60      University  of  California  Publications  in  Agricultural  Sciences    [Vol.  1 

of  copper  per  acre  a  year,  the  net  addition  of  copper  to  the  soil 
would  be  approximately  ten  pounds,  or  about  0.00025  per  cent. 
It  would  therefore  require  about  forty  years  to  accumulate  0.01 
per  cent  of  copper  in  the  surface  foot  of  soil.  Inasmuch  as,  under 
field  conditions,  this  is  not  an  injurious  amount,  there  is  little 
likelihood,  considering  the  district  in  a  general  way.  that  tbe 
small  residues  of  copper  now  coming  down  stream  will  accumu- 
late to  an  injurious  extent  within  a  reasonable  period  of  time. 
Incidentally,  it  is  of  interest  to  note  the  large  total  losses  of 
copper  (3094  lb.  and  9720  lb.  per  day  observed)  formerly  result- 
ing from  mining  operations  in  the  district. 

Possible  Effects  upon  Health 
With  reference  to  the  question  of  poisonous  effects  upon  man 
and  animals  of  dissolved  copper  in  irrigating  and  well-waters, 
such  effects,  in  general,  are  much  less  upon  animals  than  upon 
plant  life.  Moore  and  Kellerman  state,  tor  instance,  that  0,02 
gms.  of  copper  may  be  absorbed  daily  by  a  man  with  safety.11 
This  amount  of  copper  would  he  contained  in  five  gallons  of 
water  containing  one  part  per  million  of  copper,  the  Largest 
amount  of  copper  observed  in  a  well-water  in  the  district  studied 
lieiiiLr  <•. •">:'>  p. p. in.  It  is  of  interest  in  this  connection  to  note  a 
belief  of  the  copper  miners  of  the  Rio  Tinto  in  southern  Spain, 
where  the  wells  are  impregnated  with  copper,  that  one  part  of 
copper  per  million  of  drinking  water  is  permissible,  hut  that  two 
parts  per  million  result  in  "copper  colic."  ""  In  view  of  experi- 
ments upon  human  subjects,  however,  it  is  more  than  likely  that 
deleterious  effects  observed  are  due  to  associated  compounds  in 
the  water.  It  is  of  importance  to  note  that  a  strength  of  as 
little  as  one  part  per  million  of  copper  in  pure  water  will  de- 
stroy algae,  which  are  common  in  clear  water  supplies  freely 
exposed  to  light  and  air.  This  fact  may  he  made  of  use  in  clean- 
ing ditches  and  reservoirs  of  aquatic  growth,  where  the  expense 
is  not  too  great. 

The  germicidal  effects  of  small  amounts  of  copper  in  waters 
of  the  district  studied  also  have  a  bearing  upon  human  health. 


"  U.  S.  D.  A.  Bur.  PI.  Ind.,  Bull.  64,  p.  23. 

110  Conversation  of  J.  W.  Bennie,  Clifton,  Arizona. 


1917]     Forbes:  Irrigation  Effects  of  Copper  Compounds  Upon  Crops       461 

Bacilli  of  various  species  reacting  upon  human  health  are  very 
sensitive  to  the  action  of  soluble  copper  salts.  For  instance,  in 
distilled  water  "one  part  copper  in  16,000,000  parts  water  killed 
typhoid  bacilli  in  two  hours.  In  copper  solutions  made  up  with 
tap  and  sea  water,  the  action  was  still  marked,  but  less  vigorous 
than  in  distilled  water. ' ' 12  Moore  and  Kellerman  state  that  one 
part  of  copper  sulphate  to  100,000  parts  of  water  destroys 
typhoid  and  cholera  germs  in  three  to  four  hours.13  In  milk 
supplies  as  little  as  one  part  of  copper  salts  in  2,000,000  of  water 
acts  as  an  antiseptic  against  putrescent  bacteria.14  It  seems, 
therefore,  that  there  is  a  possibility  that  the  amounts  of  copper 
observed  in  ditch  and  well-waters  in  the  district  may  have  an 
antiseptic  effect  upon  malignant  germs,  more  particularly  typhoid 
fever,  likely  to  occur  in  the  district.15 


Amounts  and  Significance  op  Copper  in  Aerial  Vegetation 

The  amounts  of  copper  found  in  aerial  parts  of  vegetation 
within  the  district  are  small,  ranging  from  a  trace  to  7.6  parts 
copper  in  1,000,000  of  dry  matter  and  averaging  3.41  parts. 
Miscellaneous  cultures  in  water,  potted  soils,  and  plots  gave 
larger  amounts  of  copper  which,  however,  were  associated  in 
most  cases  with  toxic  effects.  Table  30  (p.  462)  contains  a  sum- 
mary of  these  data. 

Even  allowing  for  errors  of  method  and  of  analysis,  the 
European  figures  (3)  seem  excessively  high,  although  the  woody 
character  of  most  of  the  samples  was  for  the  most  part  very 
different  from  that  of  the  tender  crop  plants  of  the  Arizona  series. 

Little  can  be  said  as  to  the  toxic  effects  of  the  copper  ob- 
served in  aerial  plant  parts  in  the  Arizona  samples.  The  yellow 
striping  of  copper-poisoned  corn  is  probably  a  general  symptom 
of  malnutrition  to  be  attributed  to  the  effect  of  copper  upon  root 
systems  rather  than  upon  leaves  and  stems.  In  rare  instances, 
however,  beans  and  squash  in  water  culture  showed  dark  green 


12  Biochem.  Jour.,  Aug.,  1908,  pp.  319-323. 

is  IT.  S.  D.  A.  Bur.  PI.  Ind.,  Bull.  64,  p.  43. 

1*  Jour.  Ind.  and  Eng.  Chem.,  Sept.,  1909,  p.  676. 

is  See  Bibliography,  p.  487,  references  3,  20,  21,  22. 


462      University  of  California  Publications  in  Agricultural  Sciences    [Vol.  1 


TABLE  XXX 

Summary  of  Copper  Content  of  Aerial  Vegetation 

Min.  Max.  Ave. 

No.  of        , A , 

samples  Parts  per  million  copper 

1.  Field  vegetation  from  upper  Gila....    10  trace  7.60  3.41 
Field  vegetation  from  other  sources 

in    Arizona    9  none  6.30  1.52 

2.  Corn   plants   grown    in    pots   .01-.05 

per  cent  Cu  3             6.5             21.00             13.30 

Tops    of    corn,    beans    and    squash 

grown  in  Cu  water  culture  6           11.7             32.00             22.90 

Tops  of  corn,  beans,  etc.,  irrigated 

with  copper  solutions   14.00 

Beans  in  soils  containing  Cu 9           13.0             44.00             26.00 

Squash  ditto  5           14.0             61.00             39.00 

Corn   ditto   20             4.4           239.00             42.00 

3.  Field    samples    collected    by    Leh- 

mannifl  43  0  560.00  86.00 

Field    samples    collected    by    Ved- 
rodi17 

1894    26  40.0         1350.00  257.00 

1895    26  10.0  680.00  151.00 


patches  that  may  possibly  have  been  due  to  presence  of  copper, 
inasmuch  a.s  appearances  of  this  character  are  sometimes  noted 
as  an  effect  of  the  application  of  Bordeaux  mixture.  Rain 
states,  for  instance,  that  extremely  minute  amounts  of  copper 
stimulate  formation  of  chlorophyll  in  a  cell,  and  therefore  in- 
crease the  formation  of  starch.18  Ewart,  also,  shows  that  solu- 
tions of  copper  a.s  dilute  as  1  to  30.000.000  prevent  the  action 
of  diastase  upon  starch.1"  It  is  possible,  therefore,  that  the  juices 
of  plant  tissues  containing  traces  to  239  parts  (observed)  of 
copper  in  1,000,000  of  dry  matter  may  carry  sufficient  of  this 
amount  in  solution  in  the  cell  sap  to  hinder  the  action  of  enzymes 
upon  starch,  and  thus  prevent  its  normal  translocation. 


16  Der  Eupfergehalt  von  Pflanzcn  und  Thieren  in  Kupfcrrcichen  Gegen- 
den,  Lehmann  Archiv  fur  Hygiene,  vol.  27,  pp.  1-17,  1896. 

17  Quoted  in  Brenchley,  Inorganic  Plant  Poisons,  p.  17,  1914. 
is  Bain,  Tenn.  Agr.  Exp.  Sta.,  vol.  15,  Bull.  2,  p.  93,  1902. 
isEwert,  Zeitschr.  fur  Pflanzenkrankh.,  vol.  14:3,  p.  135,  1904. 


1917]     Forbes:  Irrigation  Effects  of  Copper  Compounds  Upon  Crops       463 

Amounts  and  Significance  op  Copper  in  Root  Systems 

Of  far  more  and  unmistakable  importance  is  the  effect  of 
copper  on  root  systems  of  plants.  Under  all  conditions,  whether 
grown  in  water  culture,  in  pots,  plots,  or  as  field  crops,  the  root 
systems  of  plants  contain  much  greater  amounts  of  copper  than 
do  the  aerial  portions,  as  is  shown  briefly  in  the  following  con- 
densation of  results  : 

TABLE  XXXI 
Summary  of  Copper  Content  of  Tops  and  Eoots  of  Plants 

Cu  in  p. p.m. 

No.  of      , A x 

samples      Tops  Roots  Ratio 

Coin,  beans,  and  squash  in  water  cul- 
tures, poisoned  but  living  3         22.00         103.00         1  to  4.7 

Ditto— killed    by    copper    3         23.00         268.00         1  to  11.6 

( lorn  grown  in  soil  containing  .01  per 

cent  of  Cu  as  Cu(OH)2CuC03  1  6.50         152.00         1   to  23 

Corn  grown  in  soil  containing  .025  per 

cent  Cu  as  Cu(OH)2.CuC03 1         21.00         728.00         1   to  35 

Corn  grown  in  soil  containing  .05  per 

cent  Cu  as  Cu2S  1         12.50         171.00         1   to  14 

Bean  series  grown  in  soils  containing 

Cu  as   pptd.   carbonate   .0025   to   1.5 

per  cent  Cu  in  soil 9         26.00       1431.00         1  to  55 

Corn  series  grown  in  soils  containing 

Cu   as   Cu2S   .01    to   1    per   cent   Cu 

in   soil   7         51.00         702.00         1  to  14 

Corn  series  grown  in  soils  containing 

Cu  as  chrysocolla,  .05  to  1  per  cent 

Cu  in  soil  3         13.00         266.00         1  to  20 

Corn   series   grown   in   soils   containing 

Cu  as  pptd.  carbonate,   .0025   to   .05 

per  cent  Cu  in  soil 4         13.00         416.00         1  to  32 

Excluding  samples  grown  in  water  cultures,  the  roots  of 
which  were  cleaned  with  4  per  cent  HC1,  probably  with  loss  of 
some  copper,  the  root  systems  of  experimental  cultures  contained 
averages  of  from  fourteen  to  fifty-five  times  as  much  copper  as 
the  aerial  portions  of  the  plants.  Furthermore,  fine  roots  of  corn 
were  found  in  one  instance  to  contain  about  three  times  as  much 
copper  as  coarse  roots  of  the  same  sample,  and,  finally,  the 
maximum  amount  of  copper,  as  determined  both  by  analysis  and 
by  observation,  in  water  cultures,  was  found  in  the  root  tips 


464      University  of  California  Publications  in  Agricultural  Sciences    [Vol.  1 

of  plants  affected  by  copper.  Analyses  of  water  cultures  of  corn, 
pea.s,  and  wheat  showing  slight  toxic  effects  gave  the  following 
ratios  of  copper  in  tops,  root  systems,  and  root  tips: 

Water  cultures  (u  in  p. p.m. 

showing  slight  , K v 

toxic  effects                               Tops           Roots  exclusive  of  tips  Root  tips 

Corn    27.00                     91.00  545.00 

Peas    17.00                 1400.00  3428.00 

1680.00 

Wheat  130.00                   207.00  2811.00 

The  root  tips  in  this  material,  by   means  of  caustic   potash 
(the  biuret  reaction)  and  potassium  ferrocyanide.  show  the  char- 
acteristic purple  and  dark-red  reactions  due  to  copper.     In  the 
former  ease  not  only  copper,  but  copper   in   combination    with 
prol (ids,  is  indicated — the  purple  color  being  due  to  the  biuret 
test,  which  identifies  both  copper  and  proteids  simultaneously. 
Tn    roots   grown    in    water   culture,    and    then    subjected    to    the 
action   of  dilute  copper  solutions,   the   location   of  copper   in   a 
poisoned   root   system  can   he  seen   under  a   low    power  witli   con- 
siderable exactness.     The  purple  of  the  biurel   test   begins  very 
definitely    with    the    growing    point    of    the    root    tip    and    fades 
out   gradually    in    comet-like    fashion    usually    within    one   or   two 
millimeters  distance  of  the  tip.     New  growing  points  in   process 
of  pushing  their  way  through  the  epidermis  along  the  sides  of 
the   roots  likewise  give  a   strong  but  very   local   biuret    reaction. 
This  combination  of  copper  (in  the  form  of  oxide)  and  proteids 
is  one  used  for  the  precipitation  of  albuminoid  nitrogen  in  chem- 
ical analysis  of  feeding  stuffs.2"     The  amount  of  copper  entering 
into  the  combination   varies  with  proteids   from   various  sources. 
As  a  rule,  animal   proteids  combine  with  much  less  copper  than 
vegetable  proteids — averaging  about  2.4  per  cent  of  copper  for 
egg  albumin.      Vegetable   proteids  combine   with    from    11.60   to 
16.97  per  cent  of  copper  oxide  and  average   11.7  per  cent   cop- 
per.'1    Ordinarily,  therefore,  a   vegetable  proteid  would   he  sat- 
urated   with    about   one-ninth    of   its   weight    of   copper;    but    its 
physiological   activities  are  disarranged  and   the  root   killed   by 
much    less  than   the  amount   required   to  saturate   the   proteid. 


20  See  Bibliography,  p.  488,  reference  48. 

21  Mann,  Chemistry  of  the  proteids,  p.  305. 


1917  I     Forltts:  Irrigation  Effects  of  Copper  Compounds  Upon  Crops       465 

For  instance,  in  samples  of  wheat  and  pea  roots  grown  in  water 
culture,  it  was  found  by  means  of  nitrogen  and  copper  deter- 
minations, using  the  factor  11.7  per  cent  copper  for  saturation 
of  albuminoids,  that  in  wheat  roots  4.96  per  cent  of  the  copper 
required  for  saturation  was  present  and  in  pea  roots  7.99  per  cent. 

It  appears,  therefore,  first,  that  copper  attacks  plant  proteids 
at  the  most  delicate  and  vulnerable  points  in  the  whole  plant 
organization — the  growing  points  of  the  root  systems;  and,  sec- 
ond, that  a  small  proportion  of  the  copper  required  for  complete 
reaction  is  sufficient  to  kill  the  protoplasm  at  these  points. 
Again,  it  is  to  be  observed  that,  especially  in  the  seedling  stages 
of  growth,  the  number  of  growing  points  is  small  so  that  only 
extremely  minute  amounts  of  copper  are  required  to  arrest  the 
growth  of  root  tips,  the  spread  of  root  systems  and  the  nutrition 
of  the  plant. 

Inasmuch,  also,  as  plants  vary  greatly  in  the  physical  struc- 
ture and  the  physiological  activity  of  their  root  systems,  includ- 
ing the  number,  delicacy  and  absorptiveness  of  their  growing 
points,  it  is  not  unlikely  that  the  varying  sensitiveness  to  copper 
salts  of  different  plants,  and  of  the  same  plant  at  different  ages, 
may  be  explained  by  these  observations.  Corn,  for  instance,  the 
most  sensitive  plant  worked  with,  is  characterized  in  its  seedling 
stages  by  a  small  number  of  vigorously  absorptive  growing 
points. 

By  means  of  the  more  delicate  dark-red  potassium  ferro- 
cyanide  test,  copper  may  usually  be  traced  through  the  vessels 
of  the  root  systems  for  considerable  distances,  showing  that  it 
is  through  these  channels  that  small  amounts  of  the  metal  finally 
reach  the  steins  and  leaves.  Here  the  maximum  amounts  of 
copper  are  found  in  the  (inter  and  upper  portions  of  the  plant, 
where  evaporation  is  most  active,  and  where  the  greatest  residuum 
of  copper  therefore  occurs.  The  potassium  xanthate  (yellow) 
and  hydrogen  sulphide  (brown)  tests  also  reveal  copper  in  root 
structures  but  are  not  so  satisfactory  for  this  purpose  as  potas- 
sium ferroeyanide.     (See  plate  9.) 

The  above  described  reactions,  which  are  so  conspicuous  in 
water-cidture  material  killed  by  copper,  are  very  obscure  or 
imperceptible  in  roots  grown  in  soils  containing  copper.     The 


466     University  of  California  Publications  in  Agriculture     -        oes    [Vol.1 

first  material,  however,  is  dead  and  more  nearly  saturated  with 
copper:  while  living  roots  from  soil  culture,  with  proteids  com- 
bined to  bu1  a  small  per  cenl  of  their  capacity  fur  cupper,  do 
not  give  satisfactory  color  tests.  These  reactions,  therefore,  do 
no1  serve  for  qualitative  determinations  of  toxic  effects  in  field 
material. 

Relations  Between  Amoi  m-  of  Coppeb  i\  Root  Systi  m-  \m> 

Km  BY     l"    Pi   INTS 

An  efforl  tu  establish  relations  between  the  amounts  of 
copper  in  parts  per  million  <>t'  dry  matter  in  pool  systems,  ami 
toxic  effects  as  shown  in  the  condition  of  aerial  portions  of  the 
plant,  was  only  partiallj  successful;  hut  a  sufficient  number  of 
observations  on  samples  of  sufficient  size  produced  under  care- 
fully regulated  conditions  would  probably  establish  such  rela- 
tions. In  the  tahles  shown  on  the  preceding  pages  there  is  a 
fair  degree  of  agreemenl  between  the  meml  each  experi- 

mental series,  the  copper  found  in  root  systems  increasing  in 
most  cases  with  the  amount  of  copper  in  the  soils  of  each  particu- 
lar series  of  cultures.  Tn  the  case  of  beans  and  corn  Lrro\\ n  in  cul- 
tures containing  copper  in  the  form  of  precipitated  carbonate, 
beans  show  a  somewhal  higher  resistance  to  toxic  effects  ami  also 
contain  larger  amounts  of  copper  in  the  pool  systems  throughoul 
the  series.  The  conditions  under  which  the  samples  were  grown 
seem  to  have,  within  limits,  more  effecl  upon  the  copper  content 
of   root    systems   than    the   amounts   ,  •    copper    in    the   soil,    as    is 

indicated  in  the  following  tabular  statemenl 

TABLE  XXXII 
Toxii   Concentrations  op  Copper  in  Soi  ■  i:        E       bms 

Co  r  rool 

Points  .it         v,  stem  »1  poinl  i  m  •'!' 

which  to]  •    bowing  point  showing 

effi  to* ffecta 

Culture  p.p.m  c  r  "i 

Corn.  seven  samples  from   field 

soils  12   :>t    }r,<; 

Corn    in    field    plots    containing 

Cu  as  sulphate 04%  296  at  .0595 

Corn  in  pot  cultures  containing 

Cu  as  carbonate  023%       748  at    .0  509  at   .02595 

Roans    in   pot   cultures  contain- 
ing Cu  as  carbonate  035%       950  at    .02595        1358  at   .0595 


1917]     Forbes:  Irrigation  Effects  of  Copper  Compounds  Upon  Crops       467 

In  this  statement,  for  instance,  field  samples  of  corn  roots 
grown  in  soil  containing  0.07  per  cent  of  copper  contained  only 
42  p. p.m.  of  copper  in  dry  matter,  while  a  plot  sample  grown  in 
soil  containing  .025  per  cent  of  copper  contained  245  p. p.m.  of 
copper  in  dry  matter,  and  corn  grown  in  pot  culture  containing 
0.02  per  cent  of  copper  in  soil  contained  748  p. p.m.  of  copper  in 
dry  matter. 

These  differences  may  be  due  to  the  coarser  root  systems  of 
plot  and  field-grown  samples,  this  condition  being  associated  with 
relatively  small  amounts  of  copper  in  dry  matter.  In  view  of  the 
great  labor  involved  in  preparing  root  samples  for  analysis  and 
the  very  variable  results  obtained  from  copper  determinations 
made  upon  such  material,  there  seems  to  be  little  hope  of  estab- 
lishing satisfactory  ratios  of  copper  to  dry  matter  for  the  pur- 
pose of  determining  that  a  sample  of  field  material  has  been 
injured  by  copper.  It  is  probable,  however,  that  for  comparative 
purposes,  pot  cultures  of  field  soils  conducted  under  uniform 
and  carefully  regulated  conditions,  with  standard  plants  of 
known  behavior,  may  yield  figures  of  comparative  value  in  de- 
termining the  character,  toxic  or  otherwise,  of  a  soil  containing 
copper.  Corn  is  an  excellent  summer-growing  plant  for  the  pur- 
pose, inasmuch  as  it  shows  toxic  effects  easily,  grows  rapidly,  and 
affords  abundant  root  materials  for  analytical  determinations. 
For  winter  cultures,  wheat  serves  well.  Both  plants  are  repre- 
sentative of  standard  crops  for  the  region  under  discussion. 

Pathological  Effects 

Pathological  effects  in  tops  and  roots  may  confirm  to  a  con- 
siderable extent,  the  fact  that  a  plant  has  been  poisoned  by  cop- 
per. The  lengthwise  yellow  striping  of  corn  and  wheat  leaves 
due  to  toxic  amounts  of  copper  is  not  distinctive  since  the 
same  appearances  may  result  from  various  other  conditions  in- 
ducing malnutrition,  such  as  those  mentioned  on  a  preceding 
page.  Usually,  however,  careful  observation  will  identify  or 
eliminate  these  other  disturbing  factors. 

Root  systems  grown  in  coppered  soils  are  also  conspicuously 
injured,  being  stunted  in  growth,  of  harsh  and  crinkly  texture 


468      University  of  California  Publications  in  Agricultural  Sciences    [Vol.  1 

and  (in  the  case  of  corn)  showing  characteristic  proliferated  root 
tips.  The  epidermis  is  thick  and  rough  and  the  cells  in  longi- 
tudinal tangential  section  contract  from  the  oblong  toward  the 
circular  form.  Here,  again,  other  factors,  such  as  alkali  salts  in 
excess,  may  lead  to  similar  appearances ;  and  these  must  be 
eliminated  in  a  diagnosis  of  copper  injury. 

Soil  Conditions  Relating  to  Toxic  Effects  of  Copper  upon 

Plants 

Certain  conditions  favor,  others  oppose  the  toxic  action  of 
copper  under  field  conditions,  the  general  tendency  being  to 
modify  or  do  away  with  toxic  effects,  where  the  amounts  of  copper 
are  not  excessive. 

Carbon  dioxide  in  the  soil,  alone  and  in  conjunction  with  cer- 
tain salts  (NaCl,  Na2S04)  tends  to  form  solutions  of  basic  cop- 
per carbonate.  Carbonates  (Na2C03,CaC03)  lessen  the  solubil- 
ity of  basic  copper  carbonate  in  carbon  dioxide  and,  therefore, 
the  toxicity  of  copper  compounds  in  soils  containing  these 
carbonates.22 

Coarse,  sandy  soils  favor  toxicity  by  permitting  free  move- 
ment of  solutions  and  because  the  withdrawal  in  them  of  copper 
from  solution  by  physical  and  chemical  reactions  is  minimum.23 

Tlie  character  of  I  In  com  pound  of  copper  to  which  roots  are 
exposed  is  important.  In  pot  cultures  of  precipitated  carbonate 
of  copper,  of  sulphide  in  the  form  of  chalcocite  pulverized  to  go 
through  a  100-mesh  sieve,  and  of  silicate  in  the  form  of  chryso- 
colla  pulverized  to  100-mesh,  toxic  effects  appeared  with  corn  as 
follows : 

Pot   culture  of  corn;   Cu  in   form   of  pptd.   carbonate — showing  toxic 

effects  at  .023%  Cu  in  soil 
Pot  culture  of  corn;  Cu  as  chalcocite,  100-mesh — showing  toxic  effects 

at  .08%  Cu  in  soil 
Pot  culture  of  corn;  Cu  as  ehrysocolla,  100-mesh — showing  toxic  effects 

at  .08%  Cu  in  soil 

The  precipitated  carbonate  is  not  only  more  soluble  in  car- 
bon dioxide  than  in  chalcocite,  but  also  more  easily  acted  upon 


22  See  Bibliography,  p.  487,  reference  12. 

23  See  Bibliography,  reference  18. 


1917]     Forbes:  Irrigation  Effects  of  Copper  Compounds  Upon  Crops       4(>9 

by  the  acids  of  plant  roots  than  chalcocite  or,  probably,  ehryso- 
colla.  Under  field  conditions,  copper  in  tailings  is  originally 
mostly  in  the  form  of  sulphides,  chiefly  chalcocite,  which  oxidizes 
only  slowly  to  sulphate  in  presence  of  water  and  air.  Chalcocite, 
3.2  grams,  shaken  up  with  600  c.c.  of  water,  and  air,  for  twenty- 
eight  days,  yielded  only  16  mg.  of  soluble  copper.  The  soluble 
sulphate  in  contact  with  silicates  and  carbonates  of  the  soil  is 
converted  to  insoluble  forms.  The  process  is  gradual  and  the 
amount  of  soluble  copper  present  at  any  one  time  is  small. 

The  tilth  of  the  soil  is  significant.  A  pot  culture  very 
thoroughly  mixed  with  0.1  per  cent  of  copper  as  carbonate  re- 
sulted in  badly  poisoned  plants  containing  about  four  times  as 
much  copper  in  root  systems  as  in  a  lumpy  mixture  of  soil  con- 
taining the  same  amount  of  copper.  The  heavy  tailings  clay, 
with  which  copper  is  chiefly  associated  in  the  district  studied, 
tends  to  remain  in  lumps  and  masses,  thus  minimizing  toxic- 
effects  of  contained  copper  compounds. 

In  water  cultures  toxic  effects  of  copper  salts  are  lessened 
by  salts  contained  in  well-water  or  in  nutrient  solutions.  This 
is  due,  in  part,  to  the  presence  of  other  ions,  the  effect  of  which 
is  to  decrease  the  ionization  of  copper  salts,  with  consequent 
decrease  in  toxicity.  This  observation  applies  to  soil-water 
solutions  which  contain  considerable  amounts  of  alkali  salts.  It 
is  of  interest  in  this  connection  to  note  that  certain  combinations 
of  salts  representing  complete  mineral  nutrients  exert  maximum 
antitoxic  action  to  copper  salts  ;24  and  that  therefore  a  fertile 
soil  containing  maximum  amounts  of  plant  nutrients  will  tend  to 
minimize  toxic  effects  of  copper. 

Antagonistic  solutions,  so  called,  involving  copper,  may  also 
account  for  a  decrease  in  toxicity.  By  reason  of  a  property  of 
the  semipermeable  membranes  of  root  systems,  ions  may  be  either 
more  readily  or  less  readily  allowed  to  penetrate.  When  pene- 
tration is  decreased  through  the  addition  of  ions  of  other  soluble 
salts  this  salt  is  said  to  be  antagonistic  in  character.  Copper 
is  thus  antagonized  by  sodium  and  potassium  salts,  of  which  the 
soluble  salt  content  of  the  soil  is  chiefly  composed.25 


2*  A.  Le  Eenard,   Essai  sur  la  valeur  antitoxique  de  1 'aliment  complet 
et  incomplet.     Abstracted  in  Science  n.  s.  vol.  28,  no.   712,  p.  236,  1908. 
25  See  Bibliography,  p.  488,  references  35-44,  52. 


470      University  of  California  Publications  in  Agricultural  Sciences    [Vol.  1 

Physical  attractions,  or  adsorptive  effects,  also  account  for 
a  very  considerable  lessening  of  the  amount  of  dissolved  copper 
salts,  in  contact  with  soil  particles.  Jensen,  for  instance,  finds 
that  a  dilute  copper  solution  is  ten  times  as  toxic  in  the  free  con- 
dition as  when  it  is  mixed  with  an  artificial  quartz  soil,  that  is 
to  say,  the  quartz  reduces  the  toxic  effects  about  nine-tenths.  In- 
asmuch as  the  reduction  in  toxicity  is  a  function  of  the  solid 
surface  to  which  the  soluble  salts  are  exposed,  the  finer  the  state 
of  division  of  a  soil  the  more  will  be  the  adsorption  and  the  less 
will  be  the  toxic  effects  of  a  stated  copper  solution.26 

The  age  of  plant  roots  markedly  affects  their  susceptibility 
to  copper  salts.  Young  and  tender  roots,  containing  large 
amounts  of  protoplasm,  are  much  more  quickly  and  easily 
poisoned  than  old  and  comparatively  fibrous  structures  contain- 
ing a  small  proportion  of  protoplasmic  materials.  This  may  be 
due  to  differences  in  the  thickness  of  cell  walls  protecting  the 
cell  contents  from  outside  substances ;  it  may  be  due  to  a  different 
degree  of  permeability  of  the  protoplasm  of  older  roots  to  copper 
salts;  or  it  may  be  due  to  lessened  reactivity  due  to  changed 
chemical  character.  In  any  case,  this  observation  indicates  a 
distinctly  greater  resistance  to  copper  in  soils,  of  older,  more 
fibrous,  and  possibly  intrinsically  more  resistant  root  systems. 
Different  species  of  plants  also  show  varying  degrees  of  resistance 
to  copper  salts.  In  pot  cultures,  peas  are  distinctly  more  re- 
sistant to  precipitated  carbonate  of  copper  than  corn.  Different 
plants  of  the  same  species  also  show  a  certain  amount  of  indi- 
viduality with  reference  to  absorption  of  copper. 


Stimulation 

Not  only  do  the  various  influences  described  above  lessen  the 
toxic  effects  of  copper  upon  plants,  but  it  is  possible,  also,  that 
the  amounts  of  copper  may  be  decreased  in  the  field  to  the 
point  at  which  stimulating  effects  occur.  As  shown  in  the  dis- 
cussion of  water  cultures  on  preceding  pages,  extreme  dilutions 
of  copper  salts  in  distilled  water,  for  instance,  1  part  to  100,- 


26  G.  H.  Jensen,  Botanical  Gazette,  vol.  43,  p.  11,  Jan.,  1907. 


1917]     Forbes:  Irrigation  Effects  of  Copper  Compounds  Upon  Crops       471 

000,000,  caused  increased  growth  of  root  tips  growing  in  these 
solutions.  This  observation  accords  with  those  of  some  other 
experimenters,  not  only  with  copper  solutions  but  with  solutions 
of  various  other  metals,  and  bears  a  certain  analogy  to  stimulat- 
ing effects  upon  animals  observed  with  very  small  amounts  of 
poisons,  such  as  arsenic  and  strychnine.  Stimulation  was  also 
observed  in  the  case  of  certain  pot  cultures  watered  with  dilute 
copper  solution  in  such  a  way  that  these  solutions  were  filtered 
through  a  thin  layer  of  soil  before  they  reached  the  plant  roots. 
Under  these  conditions  a  portion  of  the  root  systems  must  come 
in  contact  with  extremely  dilute  copper  solutions  residual  from 
the  reactions  of  copper  salts  with  the  soil.  As  in  the  case  of 
water  cultures,  these  extremely  dilute  solutions  must  have  ex- 
erted the  stimulating  effects  which  were  apparent  in  several 
cultures  made  in  this  manner. 

In  the  case  of  pot  cultures  also,  in  which  stated  amounts  of 
copper  were  uniformly  mixed  throughout  the  soil,  apparent  stim- 
ulation of  growth  was  occasionally  observed ;  for  instance,  with 
0.01  per  cent  of  copper  in  the  form  of  precipitated  carbonate  in 
a  culture  of  corn. 

A  satisfactory  explanation  of  stimulation  effects  is  not  avail- 
able. It  is  to  be  supposed  that  stimulation  in  a  soil  culture 
in  which  copper  sulphate  is  used  may  be  explained  by  the  action 
of  the  S04  ion  upon  the  soil  in  releasing  plant  food  for  the  use 
of  the  plant.  However,  such  stimulation  is  seen  in  water  cultures 
where  this  does  not  occur.  Lipman27  has  observed  that  under 
certain  conditions  the  nitrifying  flora  of  soils  is  stimulated  by 
salts  of  copper,  zinc,  iron  and  lead.  Such  stimulation,  through 
increased  elaboration  of  nitrates,  may  account  for  the  behavior 
of  cultures  showing  increased  growth.  Stimulation  effects,  there- 
fore, which  undoubtedly  occur  both  in  water  and  in  soil  cultures, 
are  perhaps  due  to  more  than  one  different  cause — to  chemical 
and  bacterial  agencies  in  soils,  and  to  a  pathological  disturbance 
in  water  cultures.28 

Taking  into  account  the  very  minute  amounts  of  copper  salts 
with  which  stimulated  growth  is  associated,  and  the  very  gradual 


-'  Lipman,  C.  B.,  and  Burgess,  P.  S.,  Univ.  Calif.  Publ.  Agr.  Sci.,  vol.  1, 
no.  6,  pp.  127-139,  1914. 

as  See  Bibliography,  pp.  487-488,  references  2,  4,  27,  33,  53,  45. 


472      University  of  California  Publications  in  Agricultural  Sciences    [Vol.  1 

addition  of  copper  to  new  ground  that  may  occur  through  irri- 
gating waters,  it  is  not  impossible  that  in  favorable  situations  an 
actual  increase  in  vegetable  growth  in  the  field  due  to  copper 
may  take  place ;  but  it  is  not  possible  in  the  field  to  prove  this 
supposition  because  of  many  other  factors,  the  effects  of  which 
prevent  trustworthy  observation. 


Field  Observations 

In  view  of  the  many  factors  influencing  results  in  the  field, 
some  leading  towards  toxic  copper  effects,  some  opposing  toxic 
effects,  and  still  others  pointing  to  the  possibility  of  stimulated 
growth,  it  is  of  interest,  finally,  to  refer  to  field  conditions  as 
they  have  existed  in  irrigated  lands  under  the  Clifton-Morenci 
mines  for  the  twelve  years  during  which  the  district  has  been 
under  observation.  At  the  beginning  of  this  period,  in  1904, 
considerable  accumulations  of  copper-bearing  tailings  were  evi- 
dent, more  particularly  at  the  heads  of  alfalfa  fields,  where  they 
sometimes  attained  a  thickness  of  as  much  as  ten  inches  or  more. 
These  blankets  usually  thinned  out  and  disappeared  between  100 
and  200  feet  from  the  head  ditches,  leaving  crops  in  lower  por- 
tions unaffected.  Deposits  of  river  sediments  were  observed  in 
other  irrigated  districts  not  affected  by  mining  detritus.  The 
growth  of  alfalfa  was  more  depreciated  by  the  denser  and  thicker 
tailings  blankets;  and  yellow  foliage  of  young  grain  and  young 
corn  was  considerably  in  evidence  in  tailings,  but  not  as  an  effect 
of  ordinary  sediments.  In  1908,  the  tailings  were  impounded, 
and  some  of  the  best  farmers  began  the  practice  of  cultivating 
alfalfa  to  break  up  the  old  accumulations,  incorporate  them  with 
the  soil,  and  secure  better  penetration  of  water  and  air  to  the 
roots  of  the  crop.  Following  this  procedure  the  stunted  growth 
at  the  heads  of  alfalfa  lands  has  considerably  but  not  yet  en- 
tirely recovered.  Patches  of  yellow  young  barley,  wheat,  and 
oats  are  still  to  be  observed  on  old  tailings  deposits;  but  as  the 
plants  become  older  they  become  normal  in  appearance,  and 
yield  apparently  normal  crops.  These  observations,  which  may 
be  repeated  many  times  in  the  course  of  a  day's  reconnaissance 
in  the  district,  from  May  to  September  for  alfalfa,  and  February 


1917]     Forbes:  Irrigation  Effects  of  Copper  Compounds  Upon  Crops       473 

to  May  for  grain,  may  be  explained  by  the  following  consider- 
ations :  The  wedge-shaped  deposit  of  tailings  indicated  in  the 
diagram  (fig.  15)  at  first  so  obstructed  access  of  water  and  air 
to  alfalfa  root-systems  that  only  stunted  development  was  pos- 
sible either  of  roots  or  tops.  With  an  annual  cultivation  of  this 
blanket  and  the  incorporation  of  river  sediments  and  better 
penetration  of  irrigating  waters,  deleterious  effects  tend  to  dis- 
appear and  the  crop  again  approaches  normal. 

Similar  land  when  plowed  for  grain  contains  most  of  the 
copper  associated  with  old  tailings  at  the  surface  of  the  soil. 
Young  grain,  therefore,  with  shallow  and  susceptible  root  sys- 


irCiiti^---^ »^^ri^^^iA;j-'-.-v4ir 


Fig.    15. — Diagram   showing   behavior    of   root   systems    under   influence 
of  tailings  blanket. 

terns,  at  first,  if  ever,  shows  effects  of  copper  in  the  soil, 
recovering  as  root  systems  penetrate  to  greater  depths  where 
they  encounter  uncontaminated  soil. 


Effects  of  River  Sediments 

With  reference  to  the  further  trend  of  copper  effects  upon 
vegetation  in  the  district,  assuming  the  permanent  exclusion  of 
solid  tailings  but  a  constant  addition  of  about  one  part  of  copper 
to  one  million  of  irrigating  water  used,  it  is  of  interest  to  take 
into  account  the  diluting  effect  of  river  sediments  upon  copper 
compounds  in  the  district. 

In  four  acre-feet  of  Gila  River  water,  these  sediments  will 
amount  to  about  eighty  tons  per  acre  a  year,29  of  which  amount 
the  ten  pounds  of  copper  contributed  in  irrigating  waters  is  only 
0.006  per  cent. 


-'»  Forbes,  R.  H.,  Ariz.  Agr.  Exp.  Sta.  Bull.  53,  p.  61. 


474      University  of  California  Publications  in  Agricultural  Sciences    [Vol.  1 

Irrigating  sediments  alone,  therefore,  considered  in  their 
general  relation  to  amounts  of  copper  which  cannot  be  prevented 
from  reaching  irrigated  fields,  are  sufficient  in  quantity  to  re- 
duce ultimately  the  amounts  of  copper  observed  below  0.01  per 
cent  in  the  soils  of  this  district.  Since  0.01  per  cent  is  a  safe 
minimum,  river  sediments,  alone,  incorporated  with  the  soil  are 
probably  sufficient  to  ameliorate  gradually  existing  accumula- 
tions of  copper  salts  and  to  take  care  of  further  contributions 
in  soluble  form  which  cannot  at  present  be  avoided. 

Effect  of  Cultivation  upon  Alfalfa 

Finally,  it  is  of  interest  to  observe  the  improvement  in  a 
field  of  alfalfa,  in  the  district  studied,  between  the  years  1!)0."> 
and  1916. 

June  23, 1905,  the  writer  carefully  measured,  cut  and  weighed 
a  representative  plot  of  alfalfa  in  William  Gillespie's  field  near 
Solomonville,  Arizona.  This  field  was  suffering  from  an  accu- 
mulation of  tailings,  the  depreciation  in  yield  at  the  upper  ends 
of  alfalfa  lands  being  conspicuously  evident.  Following  the 
exclusion  of  tailings  from  the  irrigating  supply  in  1908,  and  witli 
a  cultivation  each  winter  witli  a  disk  or  a  spring-tooth  harrow, 
the  condition  of  the  field  gradually  improved  until,  June  13,  1916, 
the  writer  returned  and  again  measured,  cut,  and  weighed  the 
identical  plot  of  alfalfa  that  had  shown  bad  effects  eleven  years 
before.  Following  are  the  data,  with  diagrams,  relating  to  these 
two  cuttings  of  alfalfa,  which  are  representative  for  the  district 
within  which  tailings  were  deposited. 

1.  Alfalfa  seriously  affected  b>/  taiUngs,  Jinn    23,  190J. 

Three  lands  in  William  Gillespie's  field  east  of  house,  near 
Solomonville,  under  Montezuma  Ditch,  out  of  Gila  River.  A  good 
stand  of  alfalfa  five  years  old.  Heavy  adobe  soil;  field  never 
disked. 

The  three  lands  observed  were,  over  all,  95  feet  wide,  and 
divided  into  plots  100  feet  long  from  top  to  bottom  of  field.  Ten 
feet  next  the  ditch  was  discarded  because  of  banks  and  bare  spots, 
and  the  extreme  lower  portion  of  the  field  because  of  roadways. 
A  portion  of  plots  6  and  7  was  discarded  on  account  of  Johnson 
grass. 


1917]     Forbes:  Irrigation  Effects  of  Copper  Compounds  Upon  Crops       475 

Observations  were  made  June  23,  1905,  on  the  second  cutting, 
just  beginning  to  bloom,  the  field  having  been  irrigated  twice 
since  the  last  cutting.  After  stirring  and  raking,  the  yield  of 
dry  hay  was  weighed  June  24.  Weather  very  hot  and  dry.  Fol- 
lowing are  the  data  relating  to  this  series : 


Plot 

Dimen- 
sions in 
feet 

Height 

of 
alfalfa, 
inches 

Yield 
of  plot, 
pounds 

Tons 
per 
acre 

Depth  of 
tailings 
on  plot, 
inches 

Condition  of  surface 

soil  at  time  of 

cutting 

1 

95x100 

19 

240 

.69* 

1*-3| 

Dust-dry  and  somewhat 
cracked 

2 

95x100 

20 

340 

.87* 

1   -2 

Dry  and  badly  cracked 

3 

95x100 

23-25 

570 

1.31 

£-H 

Dry,   cracked   at   upper 
end 

4 

95x100 

24 

595 

1.36 

l-i 

Moist,  not  cracked 

5 

95x100 

23 

550 

1.26 

f-i 

Moist,  not  cracked 

6 

60x100 

28 

400 

1.41* 

*-i 

Moist,  not  cracked 

7 

60x100 

27 

430 

1.48* 

i-  I 

Moist,  not  cracked 

*  Corrected  for  thin  stand  and  trash. 


2.  Alfalfa  slightly  affected  by  tailings,  June  13,  1916. 

The  same  three  lands,  continuously  in  alfalfa  since  1905.  A 
perfect  stand,  thin  spots  reseeded  by  means  of  a  seed  crop  in 
1915.  The  field  had  been  spring-tooth  harrowed  each  winter  for 
about  ten  years,  especially  at  heads  of  lands,  to  break  up  the 
tailings  blanket  and  secure  better  penetration  of  irrigating  water. 

As  in  1905,  ten  feet  next  the  ditch  was  discarded,  also  the 
extreme  lower  portion  of  the  field.  Johnson  grass  had  nearly 
entirely  disappeared. 

Observations  were  made  June  13,  1916,  on  the  second  cutting, 
just  beginning  to  bloom,  the  field  having  been  irrigated  twice 
since  the  last  cutting.  After  raking  and  piling,  the  dry  hay 
was  hauled  and  weighed  June  17.  The  weather  was  moderately 
hot  and  dry;  and  conditions  generally  the  same  as  those  under 
which  the  crop  was  cut  in  1905.  Following  are  the  data  for  the 
second  series  of  observations: 


476      University  of  California  Publications  in  Agricultural  Sciences    [Vol.  1 


Plot 

Dimen- 
sions in 
feet 

Height 

of 
alfalfa, 
inches 

Yield 
of  plot, 
pounds 

Tons 
per 
acre 

Appearance 

of 

tailings 

Condition    of    soil 

at  time  of 

cutting 

1 

95x100 

36-21 

875 

2.00 

Distinct 

Surface    dusty, 
drier  soil 

2 

95x100 

22-34 

857 

1.96 

Distinct 

Surface    dusty, 
drier  soil 

3 

95x100 

34-36 

972 

2.22 

Slight 

Moist  throughout 

4 

95x100 

30-36 

910 

2.08 

None 

Moist  throughout 

5 

95x100 

31-33 

900 

2.05 

None 

Moist  throughout 

6 

95x100 

28-36 

860 

1.96 

None 

Moist  throughout 

7 

95x100 

34-37 

870 

1.98 

None 

Moist  throughout 

8 

95x100 

33-36 

910 

2.08 

Nunc 

Moist  throughout 

Comparing  these  two  statements,  and  illustrating  them  by 
means  of  the  following  diagram  (fig.  16),  it  is  evident  that  the 
depreciation  in  yield  observed  in  the  upper  plots  in  1905  has  dis- 
appeared in  1916,  the  yields  on  the  last  date  being  practically 
uniform  from  top  to  bottom  of  the  field.  Effects  of  tailings  are 
still  plainly  visible  in  plots  1  and  2  in  spots  and  patches  of  short 
alfalfa,  compensated  for,  however,  by  areas  of  stimulated  growth 
apparently  due  to  seepage  from  the  adjacent  ditch.  The  yield 
of  the  field  as  a  whole  is  also  much  improved  due  to  cultivation 
and  reseeding  of  the  field. 

In  brief  it  may  now  be  stated  that,  following  the  exclusion 
of  tailings  from  the  irrigating  waters  of  this  locality,  it  has  been 
found  possible,  in  this  carefully  observed  case,  to  overcome  the 
deleterious  effects  of  tailings  deposits  upon  alfalfa,  slowly  but 
almost  entirely,  in  about  ten  years. 

Thus,  co-operation  between  miners,  in  restraining  tailings 
from  irrigating  streams,  and  those  farmers  who  cultivate  their 
alfalfa  intelligently,  effectually  disposes  of  the  most  serious  prob- 
lem that  has  arisen  in  connection  with  copper-mining  detritus. 

The  chemical  composition  of  tailings,  in  fact,  would  indicate 
that,  as  in  the  case  of  humid  region  subsoils,  when  they  arc  en- 
riched by  the  addition  of  organic  matter  and  nitrogen,  and  filled 
with  bacterial  life,  they  may  make  very  good  soil.  Following 
is  a  statement  of  the  composition  of  four  representative  samples 
of  ores  and  tailings,  with  reference  to  potash  and  phosphoric 
acid : 


1917]      Forbes:  Irrigation  Effects  of  Copper  Compounds  Upon  Crops       477 


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478      University  of  California  Publications  in  Agricultural  Sciences    [Vol.  1 


Sample 
No. 

Potash 
K,0 

Phosphoric 
acid 

PA 

Nitrogen 

N 

3491 

Sulphide    ore 

.64% 

.11% 

Doubtful 

3492 

Oxidized  ore 

.44 

.11 

3438 

Sulphide  tailings 

.79 

.29 

traces 

3439 

Oxidized  tailings 

.67 

.12 

These  ores  and  the  tailings  derived  from  them  are  rich  in 
potash,  and  contain  unexpectedly  large  amounts  of  phosphoric 
acid ;  but  nitrogen  is  almost  nil. 


SUMMARY 

1.  Copper  is  shown,  as  a  direct  effect  of  the  Clifton-Morenci 
mining  operations  in  Arizona,  to  be  distributed  throughout  water- 
supplies,  soils,  the  vegetable  and  the  animal  life  of  an  under- 
lying irrigated  district. 

2.  Smaller  amounts  of  copper  are  found  elsewhere  in  the 
State  where  the  drainage  basin  includes  mining  operations  or 
ore-bearing  areas. 

3.  Individual  plants  grown  in  water  cultures  or  in  soil  con- 
taining copper  show  a  comparatively  small,  and  probably  not 
injurious,  accumulation  of  copper  in  the  aerial  portions  of  the 
plants ;  but  the  root  systems,  carefully  cleansed  of  externally 
adhering  copper,  contain  relatively  great  amounts. 

4.  Copper  in  root  systems,  as  shown  by  the  biuret  test,  is 
largely  in  combination  with  plant  proteids,  especially  at  the 
growing  points  of  root  systems  and  near  vicinity.  The  place 
and  nature  of  the  reaction  accounts  for  the  extreme  toxicity  of 
copper  salts  to  plants.  The  varying  sensitiveness  of  plants  to 
copper  salts  may  possibly  be  explained  in  part  by  the  number  and 
disposition  of  exposed  growing  points. 

5.  Conditions  favoring  toxicity  of  copper  compounds  are  the 
presence  of  carbon  dioxide  and  certain  soluble  salts  which  assist 
in  forming  copper  solutions  that  come  into  contact  with  plant 
roots ;  coarse,  sandy  soils  favoring  free  access  of  copper  solutions 
to  plant  roots  and  minimizing  the  withdrawal  of  copper  from 
solution  by  adsorption ;  and  the  presence  of  copper  in  the  form 
of  the  more  soluble  precipitated  carbonate. 


1917]     Forbes:  Irrigation  Effects  of  Copper  Compounds  Upon  Crops       479 

6.  Conditions  opposing  toxicity  of  copper  compounds  are 
the  presence  of  copper  in  the  form  of  chrysocolla  and  chalcocite ; 
adsorption  through  contact  with  finely  divided  soil  particles ; 
reactions  with  carbonates,  silicates,  and  organic  matter  tending 
to  precipitate  copper  from  its  solutions ;  the  presence  of  certain 
soluble  salts  in  the  soil  that  overcome  toxic  action;  and  increased 
resistance  of  old  plant  roots. 

7.  The  stimulation  by  copper  of  vegetative  growth  in  pot 
and  water  cultures  has  been  observed.  Stimulated  growth  of 
crops  under  field  conditions  is  a  possibility. 

8.  Pot  cultures  may  be  used  for  comparative  determinations 
of  toxic  effects  upon  plants  of  copper  in  soils,  if  conducted  under 
rigidly  uniform  conditions.  The  copper  content  and  the  physio- 
logical response  to  copper  of  such  material  will  be  much  greater 
than  for  similar  cultures  grown  under  plot  or  field  conditions. 

9.  Copper  injury  in  field  soils  containing  doubtfully  toxic 
amounts  of  copper  may  be  diagnosed  by  a  combination  of  symp- 
toms. Facts  which  indicate  such  injury  in  a  soil  containing  0.] 
per  cent  of  copper  (more  or  less)  are:  yellow  tops  (for  winter 
grains)  in  absence  of  other  conditions  that  cause  yellow  tops; 
crinkly  root  systems  (in  absence  of  excessive  amounts  of  alkali 
salts)  ;  and  a  high  copper  content  in  dry  matter  of  root  systems. 
Combined  evidence  of  this  character,  which  may  be  observed 
in  the  district  studied,  indicates  toxic  copper  effects. 

10.  Field  observations  before  and  following  the  exclusion  of 
tailings  from  the  irrigating  water-supply  indicate  that  conditions 
in  the  district  studied  are  gradually  improving,  due  to  the  culti- 
vation of  alfalfa  and  to  the  incorporation  of  river  sediments  with 
accumulations  of  tailings.  Noticeable  toxic  effects  in  the  field 
exist  only  where  the  roots  of  young,  growing  crops  are  exposed 
to  surface  soils  containing  maximum  amounts  of  copper.  The 
general  tendency  in  the  district  is  probably  toward  decreasing 
rather  than  increasing  percentages  of  copper  in  irrigated  soils. 

11.  Methods  of  analysis  have  been  developed  for  the  purpose 
of  determining  reliably  small  amounts  of  copper  in  vegetative 
material,  particularly  in  root  sj^stems  of  plants  grown  in  soils 
containing  copper. 


480      University  of  California  Publications  in  Agricultural  Sciences    [Vol.  1 


Part  III.-APPEND1X 

METHODS  OF  ANALYSIS 
With  the  Collaboration  of  E.  E.  Free  and  Dr.  W.  H.  Ross 

Freedom  of  samples,  especially  vegetation,  from  contamina- 
tion with  adhering  copper;  and  accurate  methods  for  determin- 
ing minute  amounts  of  copper  in  sediments,  soils,  waters  and 
vegetation,  are  vital  to  the  integrity  of  the  work  recorded  in 
this  publication. 

Unusual  care  was  taken  to  perfeel  methods  for  preparation 
of  samples,  especially  roots  grown  in  media  containing  copper; 
and  refined  manipulation  in  the  determination  of  copper  reduced 
the  limit  of  error  to  approximately  .00001  gram,  or  .01  milligram. 

Reagents  and  Apparatus 

Distilled  water  of  three  derivations  was  used:  |  1  |  University 
of  Arizona  well  water  very  slowly  distilled  through  a  block-tin 
worm;  (2)  the  same,  redistilled  from  glass;  and  (3)  University 
of  Arizona  well  water  distilled  from  glass. 

Nitric  (ihd  sulphuric  acids  from  Baker  &  Adamson  were  used. 

Ammonia  and  II  s  employed  were  passed  through  two  wash 
bottles. 

Blank  determinations  from  time  to  time  with  reagents  em- 
ployed gave  no  trace  of  copper,  thus  insuring  results  obtained 
by  means  of  them. 

Copper  was  determined  by  electrolysis,  in  minute  amounts 
according  to  the  manipulation  of  E3    E.  Free 

The  balance  used  was  a  No.  2112  Eimer  and  Amend  short- 
beam  assa\    balance,  "distinctly   sensitive  to  1   200  milligram." 

.M  VXIITI.ATIOX 

Ores  and  ladings. — 1-2  gms.  were  digested  with  a  mixture  of 
8  Co..  II.\<>.  and  :»  c.c.  IK'I  on  a  hot  plate,  then  1  c.c.  II  so,  :il\<\<>\ 
and  evaporated  to  H2S04  fumes  (method  used  in  old  Dominion 
laboratory  at  Globe,  and  Copper  Queen  at  Bisbee).  Took  up 
with  water,  tillered,  neutralized  with  ammonia,  then  added  2  c.c. 
II  so,  and  a  \'cw  drops  of  Il\o   and  electrolyzed. 

Soils. — Soils  were  examined  by  two  methods; 

(a)  100  gms.  soil  was  treated  with  a  mixture  of  80  C.C  UNO 
and  20  c.c.  II, SO,  and  digested  in  a  porcelain  dish  on  a  hot  plate 
to  sulphuric  fumes;  digested  with  200  c.c.  water,  filtered,  washed 

"1»  to  about  500  r.r..  evaporate, |  to  '-'nil  c.C.  precipitated  iron  with 
ammonia,  filtered,  washed  with  about  odd  c.c.  water,  alkaline 
filtrate  reduced  by  evaporation,  acidified  faintly  with  IK'I  and 
H,S  passed  for  half  an   hour.     The  faint    black   precipitate  was 

i  Electrolytic,  determination  of  minute  quantities  of  copper    12th  (Jen 
meeting  Am.  Electrochem.  Soc,  October  17    19,    L907. 


1917]     Forbes:  Irrigation  Effects  of  Copper  Compounds  Upon  Crops       481 

allowed  to  settle  several  hours,  then  filtered,  and  the  precipitate, 
including  filter,  digested  with  5-10  c.c.  HN03  and  water  until 
copper  was  dissolved,  solution  filtered,  a  few  drops  of  H2S04 
added,  evaporated  to  fumes,  and  copper  determined  by  elec- 
trolysis with  addition  of  5-25  drops  of  HNO,. 

(b)  200  gms.  soil  was  digested  as  above  with  HNO,  and 
H2S04,  evaporated  to  fumes  of  H2S04,  digested  with  water, 
filtered  and  washed  up  to  500  c.c,  made  alkaline  with  ammonia 
and  made  up  to  1000  c.c.  After  settling,  500  c.c.  or  100  gms. 
aliquot,  was  filtered  off  and  copper  determined  as  in  (a). 

Waters. — Waters  were  evaporated  to  dryness,  the  residue 
digested  with  sulphuric  acid  and  water,  filtered  hot,  excess  of 
H2S04  evaporated,  filtered  into  platinum  dish,  a  few  drops  of 
HNO,  added,  and  electrolyzed. 

Vegetation. — Air-dried  samples  were  burned  in  a  small  sheet- 
iron  stove,  the  iron  of  which  was  found  to  contain  no  trace  of 
copper.  Two  samples  of  mistletoe,  difficult  to  burn,  were  reduced 
in  a  new  muffle  in  gasoline  assay  furnace.  The  charred  and 
partly  burned  material  was  moistened  with  water,  and  concen- 
trated HNO,  added  (100  to  200  c.c.)  until  effervescence  ceased, 
digested  until  in  plastic  condition,  diluted  with  hot  water  and 
filtered.  Evaporated  bulky  filtrate  to  dryness,  took  up  with 
water  and  HNO.,,  filtered  (getting  rid  of  much  organic  matter), 
added  about  20  c.c.  H,S04,  evaporated  to  H2SO+  fumes,  driving 
off  all  but  about  5  c.c.  H2S04,  added  water,  filtered  off  insolubles, 
made  up  filtrate  to  about  500  c.c,  passed  H2S,  and  proceeded  as 
usual  for  copper. 

The  completeness  of  the  extraction  of  copper  from  vegetation 
by  the  above  method  was  verified  as  follows:  The  extracted. 
charred  residue  from  2  lb.  8  oz.  of  dry  corn  leaves  and  blooms 
in  which  1.32  parts  Cu  per  million  was  found  (Sample  3529) 
was  removed  from  filter  paper  after  washing,  moistened  with 
H2S04  and  additionally  burned  in  a  porcelain  dish,  being  finally 
reduced,  after  again  moistening  with  H2S04,  in  a  platinum  dish 
in  the  muffle.  The  resulting  pink  ash  was  then  fused  with  three 
parts  of  dry  Na2CO,  (Kahlbaum)  and  poured  on  clean  porcelain. 
The  fusion  was  soaked  in  water  with  addition  of  H2S04,  evapor- 
ated nearly  to  dryness,  filtered  from  insoluble  portion  (lime, 
salts,  etc.),  again  evaporated  and  filtered,  and  a  third  time  the 
same,  finally  driving  off  excess  of  H.SO,  and  electrolyzing  as 
usual.  A  black  precipitate  of  carbon  but  no  Cu  was  obtained, 
the  same  being  true  of  a  blank  determination  on  the  Na2(JO,  used. 

Roots  of  plants  grown  in  water  cultures  or  in  soils  must  be 
most  thoroughly  cleansed  of  externally  adhering  copper,  since 
this  will  introduce  excessive  errors  where  the  content  of  copper 
is  small.  Three  methods  of  preparing  roots  for  copper  determina- 
tion were  employed : 

1.  Roots  grown  in  water  cultures  containing  copper  were 
dipped  for  about  ten  seconds  in  4  per  cent  HC1,  immediately 


482      University  of  California  Publications  in  Agricultural  Sciences    [Vol.  1 

washed  in  copper-free  water  and  dried.  Careful  observation  in- 
dicated that  adhering  copper  salts  deposited  from  water  solution 
were  completely  removed  by  this  treatment.  It  is  probable  that 
the  acid  penetrates  plant  tissues  somewhat  in  the  time  employed 
and  removes  some  copper.  The  results  are,  therefore,  probably 
severely  conservative. 

2.  Roots  grown  in  soil  cultures  containing  copper  cannot  be 
safely  cleansed  with  HC1,  which  does  not  readily  dissolve  silicates 
and  sulphides  of  copper,  and  which  cannot  be  allowed  to  remain 
in  contact  with  plant  roots  for  more  than  a  few  seconds. 

Carbon  dioxide  in  water  was  finally  selected  as  a  mild,  slow 
but  finally  effective  solvent  for  the  purpose.  Samples  of  roots 
were  first  very  thoroughly  washed  in  copper-free  well-water,  then 
placed  in  five-liter  jars  with  ground  glass  covers,  a  stream  of 
washed  C02  passed,  the  jars  shaken  and  treatment  with  C02 
repeated  until  the  water  was  saturated,  then  allowed  to  stand 
witli  occasional  shaking  for  twenty-four  hours.  The  solution 
was  then  siphoned  or  filtered  off  and  the  treatment  repeated 
until,  on  evaporating  the  bulky  filtrates,  no  more  copper  was 
found.  To  prevent  putrefaction  during  long-continued  washings, 
a  pinch  of  thymol  was  added  to  each  washing.  From  nine  to 
thirty-one  washings  were  found  necessary  to  cleanse  plant  roots 
thoroughly,  the  process  being  laborious  and  time-consuming. 
When  the  sample  yielded  no  more  copper  to  wash  waters  it  was 
dried,  burned  and  copper  determined  according  to  the  method 
for  small  amounts  in  plant  ashes. 

Following  is  a  record  of  washings  for  examples  of  roots 
cleaned  by  this  process: 

(1)  Corn  roots  grown  in  a  pot  culture  of  soil  containing  0.01 
per  cent  of  copper  as  basic  carbonate. 

Quantital h e  bj 
U2H  test  electrolysis 

First  wash  distinct 

Fifth  wash  distinct 

Ninth  wasli  doubtful  1  liter  of  filtrate         no  Cu 

(2)  Corn  roots  grown  in  a  pot  culture  of  soil  containing  0.05 
pei-  cent  copper  as  Cu2S. 

Quantitative  by 
electrolysis 

Tenth  wash  2  litres  of  filtrate         .00006  gm.  Cu 

(3)  Barley  roots  from  field  soil  containing  tailings. 


Quantitative  bj 

electrolysis 

First  wash 

2.433  litres  of  filtrate 

.00035  gm.  Cu 

Second  wash 

2.531 

.00012 

Fifth  wash 

2.22 

.00009 

Sixth  wash 

2.41 

.00004 

Seventh  wash 

2.00 

.00002 

Eleventh  wash 

2.00 

.00000 

1917]     Forbes:  Irrigation  Effects  of  Copper  Compounds  Upon  Crops       483 

(4)  Coarse  roots  of  field  corn  grown  in  soil  containing  tail- 
ings. 

H2S  test  Quantitative  by 

electrolysis 

Twenty-fifth  wash  distinct 

Twenty-ninth  wash  .00005  gra.  Cu 

Thirty-first  wash  .00000 

Samples  vary  as  to  number  of  washings  required  to  remove 
the  last  trace  of  copper,  but  the  definiteness  with  which,  finally, 
copper  usually  ceases  to  be  extracted  by  C02  water  indicates 
completeness  of  the  operation.  This  is  further  emphasized  by 
the  comparatively  large  amounts  of  copper  which  are  then  found 
in  root  systems  thus  cleansed. 

3.  A  third  method  of  preparing  roots  for  copper  determin- 
ation, involving  less  labor  than  by  washing  in  C02  water,  is  as 
follows :  Cleanse  roots  thoroughly  in  clean  water  with  a  camel- 
hair  brush,  dry,  burn  and  weigh  the  ash,  then  estimate  total 
copper.  Determine  copper  in  soil  shaken  from  sample,  assume 
ash  as  all  soil  and  deduct  copper  in  this  amount  of  soil  from 
total  copper  found  in  ash.  Results  by  this  method  are  low,  but 
not  seriously  in  error  if  sample  is  thoroughly  washed. 

Pts.  Cu 
Dry  per 

Example  matter  Ash  Gms.  Cu  million 

.Sample  2a  grown  in 
soil  containing 
0.05%  copper  .3561  gm.         10.84%         .000115         322 

Ash  in  sample  .0386 

Copper  in  ash  as- 
sumed as  soil  .000019 


Net  copper  assumed  .000096         270 

The  correction  introduced  reduces  parts  per  million  of  copper 
from  322  to  270,  which  latter  figure  is  conservative  in  character. 

Of  the  three  methods  above  described,  No.  2  is  undoubtedly 
most  exact,  but  is  extremely  laborious  and  time-consuming. 


THE    DETERMINATION    OF    COPPER    IN    SMALL    AMOUNTS    OF 

PLANT  ASHES 

The  ash  is  placed  in  a  platinum  dish  without  previous  pulver- 
ization and  moistened  with  concentrated  sulphuric  acid  in  suf- 
ficient quantity  to  bring  all  parts  of  the  ash  in  intimate  contact 
with  the  acid.  The  material  is  then  thoroughly  stirred  and 
heated  on  a  sand  bath  until  fumes  of  SO<  begin  to  come  off,  then 
allowed  to  cool  and  a  sufficient  quantity  of  hydrofluoric  acid 
added  to  bring  the  acid  in  contact  with  the  whole  mass,  then 
allowed  to  stand  for  at  least  half  an  hour  and  again  heated  until 


484     University  of  California  Publication*  in  Agricultural  Sciences    [Vol.1 

S03  fumes  come  oft'.  The  material  is  now  washed  into  a  casserole, 
moistened  with  sulphuric  and  nitric  acids  and  digested  at  a 
low  heat  for  at  least  one  hour.  The  heal  is  then  increased  until 
S03  fumes  are  again  driven  oft.  The  mass  is  moistened  with 
three  to  four  times  its  bulk  <>!'  distilled  water  and  digested  at  a 
gentle  heat  from  one  to  two  hours,  filtered  hot  and  then  the  lil- 
trate  and  washings  evaporated  almost  to  dryness,  thus  driving  oft 
the  exeess  of  sulphuric  acid.  The  resulting  residue  is  taken  up 
with  hot  water  and  again  filtered  to  separate  the  solution  from 
precipitated  calcium  sulphate.  This  evaporation  and  filtration 
may  have  to  he  repeated  one.  two  or  three  times  in  order  to  gel 
the  solution  sufficiently  free  from  calcium  sulphate.  The  final 
filtrate,  which  contains  the  copper,  is  then  diluted  to  about  1">I) 
to  200  c.c.  in  a  tall  beaker,  a  small  quantity  of  hydrochloric  acid 
is  added  and  hydrogen  sulphide  passed  until  the  solution  is 
thoroughly  saturated.  During  the  hydrogen  sulphide  precipi- 
tation there  should  he  no  nitric  acid  or  nitrates  presenl  in  the 
solution.  A  large  quantity  of  organic  matter  is  also  disadvan- 
tageous and  may  be  avoided  by  evaporating  the  solution  several 
times  to  dryness  with  nitric  and  sulphuric  acids,  finishing  finally 
with  an  evaporation  with  sulphuric  acid  alone  in  order  to  drive 
off  all  t  races  of  nit  ric  acid. 

Tlie  precipitate  from  the  treatment  with  hydrogen  sulphide  is 
filtered  off.  washed  with  water  saturated  with  hydrogen  sulphide 
and  digested  with  a  small  quantity  -  to  5  C.C.  of  nitric  acid 
in  a  casserole.  The  digestion  should  he  begun  cold  and  the  heal 
era  dually  increased.  If  the  digestion  is  begun  at  a  high  tempera 
ture  the  sulphur  formed  by  the  decomposition  of  the  copper 
sulphide  will  form  a  film  of  molten  sulphur  around  the  granules 
of  copper  sulphide,  and  this  tends  to  prevent  their  solution  in 
nitric  acid.  The  precipitate  after  digestion  in  nitric  acid  should 
he  a  clear  green  or  else  a  yellow.  If  there  is  any  trace  of  dark 
Color,  brown  or  black,  it  means  that  either  organic  matter  has 
been  precipitated  with  the  copper  sulphide  precipitate,  which  is 
extremely  unlikely,  or  else  that  the  above-mentioned  sulphur  film 
has  formed  around  some  of  the  particles  of  copper  sulphide 
preventing  their  solution  in  the  nitric  acid.  If  the  latter  he 
the  case,  the  determination  may  still  he  saved  h\  placing  the 
precipitate  in  a  platinum  dish  and  heating  over  a  gentle  flame 
until  the  sulphur  is  volatilized.  The  residue  of  copper  sulphide 
or  of  copper  oxide  may  then  he  digested  in  nitric  acid.  The 
digestions  in  nitric  acid  should  not  he  carried  to  a  heat  high 
enough  to  decompose  the  copper  nitrate  Formed  by  the  solution 
of  copper  sulphide. 

After  digestion  in  nitric  acid  and  the  evaporation  of  an\ 
large  excess  of  nitric  acid,  the  residue  is  taken  up  in  hoi  wafer, 
acidified  to  contain  2  4  per  cent  nitric  acid  and  filtered  into 
a  large  platinum  dish.  •  ,  to  V2  c.c.  of  sulphuric  acid  is  added. 
and  the  solution   elect rolvzed    with   a    voltage   of    from   2   to   L"  9 


1917]     Forbes:  Irrigation  Effects  of  Copper  Compounds  Upon  Crops       485 

volts  and  a  current  not  greater  than  one  ampere.  The  voltage 
may  be  higher  than  2i/>  volts  if  necessary  but  should  not  be  high 
enough  to  raise  the  current  beyond  the  limit  given.  The  elec- 
trolysis should  be  continued  at  least  three  hours  and  preferably 
nine  to  twelve  hours.  The  dish  is,  of  course,  the  cathode.  When 
the  electrolysis  is  complete  the  electrolyte  is  washed  out  of  the 
dish  by  means  of  the  sucking-bottle  and  the  dish  is  thoroughly 
washed  with  distilled  water-.  In  ease  the  deposit  of  copper  on 
the  dish  is  spongy  and  loosely  adherent  it  is  not  safe  to  wash 
out  the  electrolyte.  In  this  case  the  copper  should  be  redissolved 
and  the  electrolysis  repeated,  using  a  little  more  sulphuric  acid. 
If  the  copper  still  refuses  to  come  down  in  adherent  form  the 
addition  of  2  to  5  c.c.  of  a  one  per  cent  solution  of  gelatine  will 
often  assist  the  precipitation.  In  ease  of  a  stubborn  refusal  of 
the  copper  to  give  an  adherent  deposit  it  is  necessary  to  dissolve 
it,  evaporate  to  dryness  with  sulphuric  acid,  and  reprecipitate 
with  hydrogen  sulphide,  continuing  the  process  from  this  point 
as  before. 

If  the  copper  refuses  to  come  down  at  all  the  trouble  is 
probably  an  excess  of  acid  in  the  solution.  This  may  be  corrected 
by  the  addition  of  a  few  drops  of  ammonia.  The  concentration 
of  acid  in  the  solution  must  lie  between  one  and  five  per  cent.  At 
least  a  small  part  of  this  should  be  sulphuric  acid  as  nitric  acid 
will  be  destroyed  in  the  course  of  the  electrolysis  if  it  alone  is 
present,  and  the  solution  may  become  alkaline  (from  NH4OH), 
which  will  prevent  proper  precipitation.  Chlorides  and  organic 
salts,  such  as  acetates  and  tartrates,  should  be  carefully  avoided. 

The  resulting  deposit  of  copper  will  probably  contain  traces 
of  carbon  and  possibly  of  platinum.  In  order  to  eliminate  these 
and  at  the  same  time  precipitate  copper  upon  an  electrode  more 
suitable  for  accurate  weighing,  a  second  electrolysis  is  made, 
using  this  time  the  dish  as  anode  and  using  as  cathode  a  small 
spiral  of  platinum  wire  suspended  from  a  hook  of  silver  (or 
platinum)  wire  which  in  turn  is  connected  to  the  battery.  The 
electrolysis  should  also  be  conducted  in  nitric  and  sulphuric 
acid  solution  and  what  is  said  above  as  to  obtaining  satisfactory 
deposits  applies  with  equal  force  here.  In  this  case,  however, 
owing  to  the  small  surface  area  of  the  cathode,  it  is  necessary  to 
work  with  very  much  smaller  currents  than  were  used  in  the 
first  electrolysis.  The  maximum  current  to  be  used  must  be  so 
adjusted  by  trial  as  to  give  bright  and  adherent  deposits.  l-100th 
ampere  and  1.8  volts  is  a  good  current  for  the  purpose.  It  is  well 
to  use  as  the  source  of  current  for  this  electrolysis  four  Edison- 
Lalande  cells  and  to  have  in  the  circuit  a  resistance  of  from  30 
to  80  ohms.  This  gives  an  electromotive  force  at  the  dish  of  about 
1.8  volts.  Two  determinations  may  be  run  in  parallel.  In  this 
case  it  is  not  permissible  to  use  a  gelatine  solution  in  order  to 
secure  satisfactory  deposits,  as  the  copper  will  be  slightly  contam- 
inated with  gelatine  and  the  obtained  weight  will  be  too  high. 


486      University  of  California  Publications  in  Agricultural  Sciences    [Vol.  1 

The  electrolysis  should  be  run  at  least  nine  hours.  When  com- 
pleted, the  electrolyte  should  be  washed  out  as  before  without 
breaking  the  current,  the  electrode  lifted  from  the  solution,  dis- 
engaged from  the  supporting  hook,  and  washed  and  dried  by 
dipping  successively  in  water,  alcohol  and  ether  and  placing  in  a 
desiccator  over  sulphuric  acid.  After  having  remained  in  the 
desiccator  for  an  hour  the  electrode  is  ready  for  weighing. 
Weighings  should  be  made  on  an  assay  (button)  balance  adjusted 
to  maximum  sensibility.  After  weighing,  the  copper  is  removed 
from  the  electrode  by  dipping  in  concentrated  nitric  acid,  and 
the  electrode  cleaned  and  dried  by  dipping  successively  in  dis- 
tilled water,  alcohol  and  ether  and  placing  in  a  desiccator.  It 
is  again  weighed  as  before  and  the  difference  of  the  two  weights 
gives  the  copper  obtained. 

The  electrolyte  (from  each  electrolysis)  which  has  been 
washed  out  of  the  dish  by  means  of  the  suction  flask,  is  evapor- 
ated to  dryness  taken  up  with  water,  acidified  with  nitric  acid 
and  tested  for  copper  by  electrolyzing,  using  the  point  of 
platinum  wire  as  cathode.  In  this  way  any  possible  loss  of 
copper  by  incomplete  precipitation  in  either  of  the  electrolyses 
is  prevented.  If  any  copper  is  found  in  this  check  test  it  should 
be  dissolved  from  the  platinum  wire,  added  to  the  solution  ob- 
tained  by  dissolving  the  copper  from  the  small  electrode,  and 
the  electrolysis  repeated  in  order  to  get  the  true  weight. 

In  case  a  quantity  of  copper  too  small  to  be  weighed  is 
obtained  its  identity  as  copper  may  be  most  easily  established 
by  electrolyzing  it  onto  the  point  of  a  platinum  wire  as  described 
above.  In  these  electrolyses  with  the  platinum  wire  as  cathode 
the  current  must,  of  course,  be  kept  low  in  order  to  obtain  satis- 
factory deposits.  If  this  precaution  is  observed  the  deposit  on 
the  platinum  wire  will  be  of  a  brilliant  red  color  and  easily  dis- 
tinguishable as  copper.  If  the  deposit  is  brownish  or  blackish 
its  identity  as  copper  may  be  established  by  the  green  flash  when 
the  point  of  the  wire  is  held  in  the  colorless  flame  of  the  Bunsen 
burner,  particularly  if  the  wire  has  been  first  dipped  in  hydro- 
chloric acid.  Nitric  acid  must  not  be  used,  as  nitric  acid  itself 
will  give  a  green  flash  in  the  Bunsen  burner  flame 

The  reagents  used  in  the  above  process  should  all  be  tested 
as  to  freedom  from  copper.  The  water  used  should  be  doubly 
distilled  and,  at  least  the  second  time,  from  glass.  All  utensils 
should  be  cleaned  by  boiling  in  nitric  acid.  Care  must  also  be 
taken  to  conduct  the  operations  in  rooms  free  from  dust  which 
might  possibly  contain  copper. 


1917]     Forbes:  Irrigation  Effects  of  Copper  Compounds  Upon  Crops       487 


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PLATE  6 

Fig.   1. — Eoot  system  of  corn  plant  injured  by  0.1  per  cent  of  copper 
added  as  copper  sulphate  to  the  soil. 

Fig.  2. — Normal  corn  root  grown  in  similar  soil  containing  no  copper. 
(Photos  by  G.  F.  Freeman.) 


[490] 


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CD 

EC 

o 


OJD 


o 
> 


o 

CO 

of 

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GD 

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but) 


. 


PLATE  7 

Fig.  1. — Individual  roots  of  corn  injured  by  0.1  per  cent  of  copper  added 
as  copper  sulphate  to  the  soil. 

Fig.  2. — Individual  root  of  corn,  normal. 
(Photos  by  G.  F.  Freeman.) 


[492] 


UNIV.    CALIF.    PUBL.   AGR     SCI.    VOL.   2 


[FORBES]    PLATE  7 


Fig.  1 


Fig.  2 


I 


♦  » 


PLATE  8 

Fig.  1. — Thickened  rootlets  and  proliferated  root  tips  of  corn  injured  by 
0.1  per  cent  of  copper  added  as  copper  sulphate  to  the  soil.     (X   3  diam.) 

Fig.  2. — Fine  roots  and  root  tips  of  corn,  normal.     (  X  3  diam.) 
(Photos  by  G.  F.  Freeman.) 


[494] 


UNIV.   CALIF.    PUBL.   AGR.    SCI.    VOL    2 


[FORBES]    PLATE  8 


Fig. 


Pie.  2 


PLATE  9 
Corn  root-tips  killed  in  a  solution  of  1  part  copper  to  100,000  of  water, 
and  colored  by  means  of  (1)  caustic  potash,  which  gives  the  violet  biuret 
reaction,  identifying  both  copper  and  protein;  (2)  hydrogen  sulphide, 
brown;  (3)  potassium  xanthate,  yellow;  and  (4)  potassium  ferrocyanide, 
red.     (  X  ±  30  diam.) 


UNIV.   CALIF.    PUBL.   AGR.   SCI.   VOL 


[FORBES]    PLATE  9 


! 


